Presensitized lithographic printing plate and method for preparing lithographic printing plate

ABSTRACT

Object: A method for preparing a lithographic printing plate directly from digital image signals with the use of a presensitized lithographic printing plate comprising a support having thereon a photosensitive layer and a light-shielding layer which can be removed imagewise with laser light is provided, wherein the light-shielding layer, which can be industrially produced readily at a moderate price can be removed sufficiently during a process of development without the need of removing a masking layer at an unexposed portion and adverse effect on a photosensitive layer. 
     Constitution: A lithographic printing plate can be obtained by making use of a presensitized lithographic printing plate comprising a support having thereon a photosensitive layer containing o-quinonediazide compound, photo-degradable or photo-polymerizable resin and water-soluble resin and a light-shielding layer containing an infrared absorbing material and a material capable of absorbing the photosensitive wavelength of the photosensitive layer and by a process comprising ablating imagewise the light-shielding layer with laser light, overall-exposing with a ray active to the photosensitive layer to cause photochemical change of the photosensitive layer in which the light-shielding layer has been removed by ablation (e.g., making alkali-soluble) and dissolving out the photosensitive layer at a non-imaging area.

FIELD OF THE INVENTION

The present invention relates to a presensitized lithographic printingplate with high definition, a method for preparing a lithographicprinting plate with the use thereof and an exposure apparatus for use inthe preparing method.

BACKGROUND OF THE INVENTION

A lithographic printing plate has been prepared by a conventional methodcomprising a process of exposing a transparent original (e.g., anegative or positive film) in contact with a printing plate such as analuminum plate or zinc plate each coated thereon with a photosensitivelayer and developing the exposed plate. A positive-workingphotosensitive lithographic printing plate, for example, comprises ahydrophilic support having thereon a photosensitive ink-affinity layercapable of being solubilized upon imagewise-exposure to an actinic ray,such as ultraviolet radiation. When exposed and developed with analkaline developer, an imaging area (nonexposed portion) remains and anon-imaging area (exposed portion) is removed to expose the hydrophilicsurface of the support. As a result, the non-imaging area is capable ofretaining water and thereby it repulses ink. On the other hand, the area(imaging area) which has not been removed through development, ishydrophobic so that it repulses water and becomes ink-receptible. Thedifference between the hydrophilic nonimaging area and the hydrophobicimaging area is employed in common lithographic printing. In anegative-working photosensitive lithographic printing plate, on thecontrary, a photosensitive layer in an exposed portion (imaging area) ishardened and a photosensitive layer in an unexposed portion (non-imagingarea) is removed by a developer so that it can be used as a lithographicprinting plate.

With regard to editing the composition of a printing material which is aprocess prior to the preparing process of the printing plate, computertypesetting systems (CTS) made up of a combination of an automatictypesetting machine and computer, electronic composing and DTP (Desk TopPublishing) have become popular with the spread of word processors andpersonal computers. The computer generated data thus-edited is usuallyprepared as an original forme of a photographic film. If a printingplate material is available which enables making the printing platedirectly from the output data of a CTS or aother electronic edtingdevice, it is possible to shorten the printing process and also saveintermediate materials. As a technique in response to the directplate-making, it has been reported that there has been developed aplate-making material using an organic semiconductor or silver saltphotographic light sensitive material. However, as it still has defectssuch as needing a new processing step and the plate-life isinsufficient, it has not yet become an acceptable substitute forpre-sensitized plates.

Thermal recording, in which an image canbe obtained directly throughthermal energy of an input signal without developing and fixing, is adry-processing system without intermediate chemical steps, therefore, itis broadly employed in facsimile and printers. Recently, there has beenemployed a thermal transfer recording system, in which thermal transferrecording can be accomplished by exposing a thermal transfer recordingmaterial to a laser beam which converts the laser beam to heat in therecording material. In this laser thermal-transfer recording system, thelaser beam, used as energy supply can be condensed to such an extentthat highly-resolution recording becomes feasible, leading to use in theprinting of art works.

With respect to the image forming technique using lasers, there havebeen proposed applications for direct thermographic plate-making. InJapanese Patent examined No. 51-6568 is disclosed a technique, in whichvapor-deposition coating of metal such as aluminum or copper, or acoating comprised of carbon black dispersed in an organicsolvent-soluble binder is usable as an ablatable light-shielding layer.

However, in the case when a metal depositin coating is used as theablatable light-shielding coating, it is problematic in that twowet-processing steps are required comprising removing a masking layer inan exposed portion and developing the photosensitive layer. Further,since a large apparatus for vapor-deposition is required for forming avapor-deposited coating over a photosensitive layer on an industrialscale, it is difficult to provide it at a competitive low price. Incases when a coating of an organic solvent-soluble binder such asnitrocellulose is used as the ablatable light-shielding layer, on theother hand, the ablatable light-shielding layer can be coated using atechnique similar to that of the photosensitive layer. However, whilecoating the shielding layer, the surface of the photosensitive layer isdissolved by an organic solvent contained in a coating solution andmixed with a part of the shielding layer, producing such problems thatsensitivity of the photosensitive layer is likely to be decreased orprinting stains are caused due to the incomplete removal of theshielding layer during development.

In view of the foregoing, the present invention was developed.Therefore, an object of the present invention is to provide a method ofpreparing a lithographic printing plate directly from a digital imagesignal without the use of any intermediate material in the plate-makingprocess. Another object of the invention is to provide a technique forovercoming the above-described problems, so that, in a method forpreparing a lithographic printing plate directly from a digital imagesignal, it is to provide a technique whereby an ablatablelight-shielding layer can be readily formed at a low cost on anindustrial scale, a process of removing only masking layer in anunexposed portion is not required, there is no adverse effect of thelight-shielding layer on the photosensitive layer and any unablatedportion of the light-shielding layer can be sufficiently removed duringthe developing process.

DISCLOSURE OF THE INVENTION

The above objects can be accomplished by the following constitution.

(1) A method for the preparation of a lithographic printing plate by aprocess comprising the steps of

imagewise exposing a presensitized lithographic printing platecomprising a support having thereon a photosensitive layer and anablatable light-shielding layer to a first light having a firstwavelength to remove an imagewise exposed portion of the light-shieldinglayer by ablation,

overall exposing the presensitized plate to a second light having asecond wavelength to cause photochemical reaction in the photosensitivelayer at portions in which the light-shielding layer has been removedand

dipping the overall exposed plate into a developer to remove theunremoved light-shielding layer and a non-imaging portion of thephotosensitive layer to obtain the lithographic printing plate.

Hereinafter, the second light having the second wavelength is referredto as an actinic ray. (An imaging portion, herein, refers to an areawhich is hydrophobic and ink-affinitive. In the case of a photosensitivelayer being positive-working, the imaging portion refers to a portionunexposed to the actinic ray and in the case of a negative-workingphotosensitive layer, it refers to a portion exposed to the actinic ray.On the contrary, a nonimaging portion refers to an area which ishydrophilic and ink-repulsive, wherein, in the case of apositive-working photosensitive layer, the non-imaging portion refers toa portion exposed to the actinic ray and in the case of anegative-working photosensitive layer, it refers to a portion unexposedto the actinic ray.)

(2) The method for preparing a lithographic printing plate described in(1), characterized in that the first light has a power density of 100000W/cm² or more and exposure thereof is made at an exposing speed of 0.4m/sec. or more.

(3) The method for preparing a lithographic printing plate described in(1) or (2), characterized in that exposure is made by a high intensityfrom the side of the light-shielding layer.

(4) A presensitized lithographic printing plate comprising a supporthaving thereon a photosensitive layer and an ablatable light-shieldinglayer, characterized in that said light-shielding layer contains acompound capable of absorbing a light having a first wavelength, acompound having an absorption in a photosensitive wavelength range ofthe photosensitive layer, thus, a compound capable of absorbing a lighthaving a second wavelength and an alkaline water-soluble resin.

(5) A presensitized lithographic printing plate comprising a supporthaving thereon a photosensitive layer and a light-shielding layerdescribed in (4), characterized in that said light-shielding layercontains a near infrared-absorbing dye and a water-soluble resin.

(6) A presensitized lithographic printing plate comprising a supporthaving thereon a photosensitive layer and a light-shielding layerdescribed in (4) or (5), characterized in that said photosensitive layercontains a o-quinonediazide compound.

(7) A presensitized lithographic printing plate comprising a supporthaving thereon a photosensitive layer and a light-shielding layerdescribed in (4) or (5), characterized in that said photosensitive layercontains a diazo compound.

(8) A presensitized lithographic printing plate comprising a supporthaving thereon a photosensitive layer and a light-shielding layerdescribed in (4), (5), (6) or (7), characterized in that said nearinfrared absorbing dye contained in said light-shielding layer iswater-soluble.

(9) A presensitized lithographic printing plate comprising a supporthaving thereon a photosensitive layer and a light-shielding layerdescribed in (4), (5), (6) or (7), characterized in that said nearinfrared absorbing dye contained in said light-shielding layer isoil-soluble, said dye being dispersed, with a oil-soluble low-molecularcompound, in a water-soluble resin.

(10) An apparatus for exposing a presensitized lithographic printingplate comprising

a means for feeding a presensitized lithographic printing plate,

a means for holding the presensitized plate,

a means for exposing selectively the presensitized plate to a highintensity light in response to an image information and

a means for exposing overall to an actinic ray to cause photochemicalreaction in the photosensitive layer.

In the above-described method for the preparation of a lithographicprinting plate, an embodiment in whicht exposure is made by a lighthaving a first wavelength having a power density of 100000 W/cm² or moreat an exposing speed of 0.4 m/sec. or more, the high intensity light islaser light, exposure by the high intensity light is made from the sideof the light-shielding layer and the light-shilding layer contains awater-soluble near infrared absorbing dye displays much more effects ofthe present invention so that it is a preferable embodiment of theinvention.

BRIEF EXPLANATION OF THE DRAWING

FIGS. 1(a) to 1(d) are schematic drawings for explaining the methof forpreparing a lithographic printing plate of the present invention.

FIG. 2 is a sectional view of an apparatus for exposing a presensitizedlithographic printing plate of the present invention.

FIG. 3 is another sectional view of an apparatus for exposing apresensitized lithographic printing plate of the present invention.

Explanation of the number:

13: Means for feeding a presensitized lithographic printing plate

15 and 31: Means for holding the presensitized plate

16 and 32: Holding member

17 and 34: means for mounting the presensitized plate

18 and 35: Pressure roll

22 and 33: Evacuation hole

23 and 37: Optical writing means

25 and 38: Overall exposing means

DETAILED DESCRIPTION OF THE INVENTION

The ablatable light-shielding layer of the present invention isfunctionally identical to a transparent original used in a preparationmethod of a lithographic printing plate known in the art. It can betherefore referred to as a masking layer.

Light having a first wavelength includes high intensity laser light,which is capable of removing the light-shielding layer of the inventionby ablation. The first wavelength is preferably not less than 500 nm. Itis preferable that a laser beam with a power density of 100000 W/cm² ormore is exposed at an exposing speed 0.4 m/sec. or more.

The term, "ablation" means to make explosively a minute hole by heatinglocally and instantaneously with light such as laser to cause volumeexpansion including gasfying, in which a part is gasfied and scatteringalso occurs partly.

Light having a second wavelength is an actinic ray such as ultravioletradiation, having a wavelength in which the photosensitive layer isallowed to be photochemically reacted. The second wavelength ispreferably less tan 500 nm.

In a method for the preparation of a lithographic printing plate of thepresent invention, a light-shielding layer is abratively removed by alight having a first wavelength and a light having a second wavelengthis exposed through removed portions (ablated holes) to causephotochemical reaction in a photosensitive layer. The term, "causechemical reaction in a photosensitive layer" is meant to cause to changethe solubility of the photosensitive layer in a developer. In the caseof a negative-working photosensitive layer, an exposed portion isphoto-polymerized or photochemically cross-linked to become insoluble ina developer and an unexposed portion remains unchanged to be soluble toa developer. An ablatively-unremoved portion in which a light-shieldinglayer is remained substantially cut off the second wavelength so as toprevent a photochemical reaction from occurring in the photosensitivelayer. The term, "substantially cut off" is meant to cut off to suchextent that, as a result of the chemical reaction, an imaging portionand nonimaging portion become differentiable with respect to thesolubility in a developer. It is preferable to cut off 97% or more ofthe second wavelength. To remove ablatively the light-shielding layer bythe light having the first wavelength, the light-shielding layer absorbspreferably 80% or more of the first wavelength.

With regard to a support used in the presensitized lithographic printingplate of the present invention, if it is superior in dimensionalstability and proof against heat source such as laser used in imagerecording, it is not limitative. Examples thereof include a thin sheetpaper such as condenser paper or glassine paper; heat-stable plasticresin films such as polyethylene terephthalate, polyamide,polycarbonate, polysulfone,polyvinyl alcohol, cellophan and polystylene;metal plates such as aluminum (including alloy thereof), zinc, iron andcupper. Among these, is preferable an aluminum plate. A preferablealuminum plate is a pure aluminum plate or alloy plate thereof whichcontains a small amount of foreign element(s). A plastic film laminatedor vapor-deposited with aluminum may be usable. The content of a foreignelement contained in aluminum alloy is preferably not more than 10% byweight. The thickness of the support is preferably 100 to 600 μm, morepreferably 200 to 400 μm.

An aluminum plate is subjected to a degrease treatment with a solvent,acid or alkali for the purpose of removing oils sticked to the surface.Subsequently, it is preferably subjected to surface treatments such asgraining and anodic oxidation, and hole-sealing, if necessary. Thesetreatments can be conducted according to the methods known in the art.

A graining treatment method includes a mechanical method andelectrolytic etching method. As the mechanical method, are cited ballpolishing, brush polishing, liquid honing polishing and buff polishing.These methods are employed singly or in combination thereof inaccordance with the composition of aluminum materials.

The electrolytic etching is carried out in a bath containing aninorganic acid such as hydrochloric acid or nitric acid. After thegraining treatment, it is optionally subjected to death mattingtreatment with the use of an alkaline or acidic aqueous solution, andthen neutralized and washed.

The anodic oxidation is conducted through electrolysis with the use of,as an electrolytic solution, sulfuric acid, chromic acid, oxalic acid,phosphoric acid, malonic acid or a mixture thereof; and an aluminumplate as an anode. The amount of anodic oxidation coating formed is 1 to50 mg/dm², preferably 10 to 40 mg/dm², more prefrably 25 to 40 mg/dm².The amount of the anodic oxidation coating can be determined, forexample, in such a manner that an aluminum plate is dipped into aphosphoric and chromic acid solution (35 ml of 85% phosphoric acidsolution and 20 g of chromium oxide are dissolved in 1 liter of water)to dissolve out the oxidation coating, and difference of the plateweight between before and after being dipped is measured.

As examples of the hole-sealing treatment are cited treament with theuse of boiled water, water vapor, silic acid and aqueous dichromatesolution. Furthermore, an aluminum support may be subjected to a subbingtreatment with the use of a water-soluble polymeric compound or aqueoussolution of a metal salt such as fluorozirconate.

On a support such as the thus-prepared aluminum plate which hashydrophilic surfaces is provided a photosensitive layer comprising knownphotosensitive composition. As the photosensitive composition, are useda positive working photosensitive composition containing ao-quinonediazide compound as a photosensitive component and a negativeworking photosensitive composition containing, as a photosensitivecomponent, a photosensitive diazo compound, photo-polymerizable compoundsuch as a monomer having an unsaturated double bond, or cinnamic acid ora photo-crosslinkable compound having a dimethylmaleimido group.

As o-quinonediazide compounds used as a positive working photosensitivecomposition, ester compounds of o-quinonediazidosulfonic acid with apolycondensate resin comprising a phenol and aldehyde (or ketone) areprefrable. The phenols include phenols such as phenol, o-cresol,m-cresol, p-cresol, 3,5-xylenol, carvacrol and thymol; dihydroxybenzenessuch as catecohol, resorcin and hydroquinone; and trihydroxybenzenessuch as pyrogallol and phloroglucide. The aldehyde includesformaldehyde, benzaldehyde, acetoaldehyde, crotonaldehyde or furfural.

As examples of the polycondensate resin are cited phenol-formaldehyderesin, p-cresol-formaldehyde resin, m-cresol-formaldehyde resin, m- andp-mixed cresol resin, resorcin-benzaldehyde resin and pyrogallol-acetoneresin. In afore-described o-quinonediazide compounds, a condensationratio of o-quinonediazidosulfonic acid to the OH-group of phenols(reaction ratio per OH group) is preferably 15 to 80%, more preferably20 o 60%.

As o-quinonediazide compounds used in the present invention, compoundsdescribed in JP-A 58-43451 may be usable. Examples thereof include a1,2-naphthoquinonediazide compound such as1,2-naphthoquinonediazidosulfonic acid ester or1,2-naphthoquinonediazidosulfonic acid imide, more concretely are cited1,2-naphthoquinonediazide compounds such as1,2-naphthoquinonediazido-5-sulfonic acid cyclohexyl ester,1-(1,2-naphthoquinonediazido-5-sulfonyl)-3,5-dimethylpyrazole,1,2-naphthoquinonediazido-5-sulfonicacid-4"-hydroxydiphenyl-4'-azo-β-naphthol ester,N,N-di-(1,2-naphthoquinonediazido-5-sulfonyl)-aniline,2'-(1,2-naphthoquinonediazido-5-sulfonyloxy)-1-hyroy-anthraquinone,1,2-naphthoquinonediazido-5-sulfonic-acid-2,3,4-trihydoxybenzophenoneester, condensate of 1,2-naphthoquinonediazido-5-sulfonic-acid-chloride(2 mol) and 4,4'-diaminobenzophenone (1 mol), condensate of1,2-naphthoquinonediazido-5-sulfonic-acid-chloride (2 mol) and4,4'-dihydroxy-1,1'-diphenylsulfon (1 mol), condensate of1,2-naphthoquinonediazido-5-sulfonic-acid-chloride (1 mol) andpurpurogallin (1 mol), and1,2-naphthoquinonediazido-5-(N-dihydroxyabiethyl)-sulfonamide, asdiscribed in J. Kosar, "Light-Sensitive System" pages 339-352 (1965),John Wiley & Sons (New York) and W. S. De Frest, "Photoresist" Vol.50(1975), McGraw-Hill (New York). Further, are cited1,2-naphthoquinonediazide compounds described Japanese Patent examined7-1953, 37-3627, 37-13109, 40-26126, 40-3801, 45-5604, 45-27345,51-13013, JP-A 48-96575, 48-63802 and 48-63803.

As o-quinonediazide compound usable in the present invention,furthermore, are cited 1,2-naphthoquinonediazido-4-sulfonic-acid estercompounds such as 1,2-naphthoquinonediazido-4-sulfonic acidcyclohexylester,1-(1,2-naphthoquinonediazido-4-sulfonyl)-3,5-dimethylpyrazole,1,2-naphthoquinonediazido-4-sulfonicacid-4"-hydroxydiphenyl-4'-azo-β-naphthol ester,2'-(1,2-naphthoquinonediazido-4sulfonyloxy)-1-hyroy-anthraquinone,1,2-naphthoquinonediazido-4-sulfonic-acid-2,3,4-trihydoxybenzophenoneester,1,2-naphthoquinonediazido-4-sulfonic-acid-2,3,4,4'-tetrahydroxybenzophenoneester, condensate of 1,2-naphthoquinonediazido-4-sulfonic-acid-chloride(2 mol) and 4,4'-dihydroxy-1,1'-diphenylsulfon (1 mol), condensate of1,2-naphthoquinonediazido-4-sulfonic-acid-chloride (1 mol) andpurpurogallin (1 mol).

The o-naphthoquinonediazide compounds as above-described may be usedsingly or in combination thereof. The proportopn of theo-naphthoquinonediazido compound contained in the photosensitivecomposition is preferably 5 to 60% by weight, more preferably 10 to 50%by weight.

The o-naphthoquinonediazido compound may singly constitute thephotosensitive layer. However, it is preferable to make use incombination with an alkali-soluble resin as a binder. As thealkali-soluble resin, there may be usable various kinds of resins knownin the art. Particularly, novolak resin and vinyl polymer having astructure unit containing a phenolic OH group are preferable.

As a novolak resin used in the present invention are cited a resinobtained by the condensation of phenols with formaldehyde in thepresence of acid catalyst. The phenols include phenol, o-cresol,m-cresol, p-cresol, 3,5-xylenol, 2,4-xylenol, 2,5xylenol, carvacrol,thymol, catechol, resorcin, hydroquinone, pyrogallol and phloroglucin.The above-described phenols are, singly or incombination, condensed withformaldehyde to obtain a resin. Particularly, preferable novolak resinsare those obtained by the condensation polymerization of at least one ofphenol, m-cresol (or o-cresol) and p-cresol, and formaldehye, forexample, phenol-formaldehyde resin, m-cresol-formaldehyde resin,o-cresol-formaldehyde resin, phenol-p-cresol-formaldehyde copolymerresinm-cresol-p-cresol-formaldehyde copolymer resin,phenol-m-cresol-p-cresol-formaldehyde andphenol-o-cresol-p-cresol-formaldehyde. Among these novolak resin,phenol-o-cresol-p-cresol-formaldehyde copolymer resin is preferable.

In the present invention, the novolak resin may be used singly or incombination thereof.

The molecular weight of the novolak resin (polystylene as standard) is2.0×10³ to 2.0×10⁴ with respect to a weight-averaged molecular weight(Mw) and 7.0×10² to 5.0×10³ with respect to number-averaged molecularweight (Mn), preferably 3.0×10³ to 6.0×10³ (Mw) and 7.7×10² to 1.2×10³(Mn).

The molecular weight of the novolak resin can be determined by GPC (GelPermulation Chlomatography). The number-averaged molecular weight (Mn)and weight-averaged molecular weight (Mw) can be determined in a manneras described in M. Tsuge, T. Miyahashi & M. Tanaka, "Nihon Kagakukaishi"(Journal of the Chemical Society of Japan) page 800-805 (1972).

With regard to the vinyl type polymer having a structure containing aphenolic OH group, the polymer, which can be obtained through thepolymerization involving carbon-carbon double bond cleavage haspreferably a structure unit represented by the following formulas (1) to(6). ##STR1##

In the formulas, R₁ and R₂, each represent a hydrogen atom, alkyl group,carboxyl group and among these is preferable a hydrogen atom. R₃represents a hydrogen atom, halogen atom, or alkyl group, and preferablya hydrogen atom or alkyl group such as methyl and ethyl. R₄ represents ahydrogen atom, alkyl group, aryl group, or aralkyl group, and preferablya hydrogen atom. A represents an alkylene group linking a nitrogen oroxygen atom with an aromatic carbon atom, which may be substituted; m isan integer of 0 to 10; and B represents a phenylene group or naphthylenegroup, each of which may be substituted. In the present invention, amongthese, is preferable a copolymer having a structure unit represented byformula (2).

The vinyl polymer above-described has preferably a copolymer typestructure. In such a copolymer, a monomer unit which can be combinedwith at least one of the structure units represented by formulas (1) to(6) includes ethylenic unsaturated olefins such as ethylene, propylene,isobutylene, butadiene or isoprene; stylenes such as stylene,α-methystylene, p-methylstylene or p-chlorostylene; acrylic acid such asacrylic acid or methaacrylic acid; unsubstituted aliphatic carboxylicacid such as itaconic acid, maleic acid or maleic acid anhydride; esterof α-methylene aliphatic carboxylic acid such as methylacrylate,ethylacrylate, n-butylacrylate, isobutylacrylate, dodecylacrylate,2-chloroethylacrylate, phenylacrylate, methyl-α-chloroacrylate,methylmethaacrylate, ethylmethaacrylate or ethylethaacrylate; nitrilesuch as acrylonitrile or methaacrylonitrile; amide such as acrylamide;anilide such as acrylanilide, p-chloroacrylanilide, m-nitroacrylanilideor m-methoxyacrylanilide; vinyl ester such as vinylacetate,vinylpropionate, vinylbenzoate or vinylbutylate; vinyl ether such asmethylvinyl ether, ethylvinyl ether, isobutylvinyl ether orβ-chloroethylvunyl ether; vinyl chloride; vinylidene chloride;vinylidene cyanate; ethylene derivative such as1-methylene-1-methoxyethylene, 1,1-dimethoxyethylene,1,2-dimethoxyethylne, 1,1-dimethoxycarbonylethylene or1-methyl-1-nitroethylene; N-vinyl compound such as N-vinylpyrrole,N-vinylcarbazole, N-vinylindole, N-vinylpyrrolidene orN-vinylpyrrolidone.

Among the monomers above-described, (metha)acrylates, aliphaticmonocarboxylic acid esters and nitrites are preferable; and methaacrylicacid, methyl methaacrylate, acrylonirile and ethyl acrylate are morepreferable.

These monomers may be bonded in the form of block or at ramdom in thevinyl polymer afore-decribed.

The proportion of the struture unit represented by formulas (1) to (6)contained in the vinyl polymer is preferably 5 to 70 mol%, moreprefrably 10 to 40 mol%.

The foregoing polymer may be incorporated in the photosensitivecomposition singly or in combination thereof.

Exemplary vinyl polymers are shown as below, in which Mw and Mn refer toa weight-averaged molecular weight and number-averaged molecular weight,respectively; s, k, l, o, m and n each represent mol % of the structureunit. ##STR2##

The proportion of the alkali-soluble resin afore-described contained inthe photosensitive composition is preferably 50 to 95 mol %, morepreferably 60 to 90 mol %.

The photosensitive composition may contain optionally an organic acid oracid anhydride. As the organic acid various kinds of organic acid knownin the art may be usable. The acid has prefrably a pKa of 2 or more,more preferably 3.0 to 9.0, most preferably 3.5 to 8.0.

These organic acids are referred to organic acids described in "KagakuBinran Kisohen", Maruzen (1966) pages 1054-1058. These compound includebenzoic acid, adipinic acid, azelaic acid, isophthalic acid, p-toluicacid, β-ethylglutaric acid, m-oxybenzoic acid, p-oxybenzoic acid,3,5-dimethylbenzoic acid, 3,4-dimethoxybenzoic acid, glyceric acid,glutaconic acid, glutaric acid, p-anisic acid, succinic acid, sebaciccid, β,β-diethylglutaric acid, 1,1-cyclobutanedicarboxylic acid,1,3-cyclobutanedicarboxylic acid, 1,1-cyclopentane-dicarboxylic acid,1,2-cyclopentanedicarboxylic acid, 1,3-cyclopentanedicarboxylic acid,β,β-dimethylglutaric acid, dimethylmalonic acid, α-tartaric acid,suberic acid, terephthalic acid, pimelic acid, phthalic acid, fumaricacid, β-propylglutaric acid, propylmalonic acid, mandelic acid,meso-tartaric acid, β-methyglutaric acid, β,β-methylpropyl-glutaricacid, methylmalonic acid, malic acid, 1,1-cyclohexanedicarboxylic acid,1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid,1,4-cyclohexanedicarboxylic acid, cis-4-cyclohexene-1,2-dicarboxylicacid, erucic acid, undecenic acid, lauric acid, n-capric acid,pelargonic acid and n-undecanic acid. Further, an organic acid having anenol structure including meludrumic acid and ascorbic acid is preferablyused. The proportion of the organic acid contained in the photosensitiveis 0.05 to 10% by weight, preferably 0.1 to 5% by weight.

With regard to the acid anhydride contained in the photosensitivecomposition, various kinds of acid anhydrides known in the art may beusable. The acid anhydride is preferably a cyclic acid anhydride,including phthalic anhydride, tetrahydrophthalic anhydride,hexahydrophthalic anhydride, 3,6-endooxy-Δ⁴ -tetrahydrophthalicanhydride, tetrachlorophthalic anhydride, glutaric anhydride, maleicanhydride, chloromaleic anhydride, α-phenylmaleic anhydride, succinicanhydride and pyromellitic anhydride. The acid anhydride is contained inthe photosensitive layer in an amount of 0.05 to 10% by weight,preferably 0.1 to 5% by weight.

The photosensitive composition contains preferably a compound capable offorming an acid or radical upon exposure to light. The compound is atrihaloalkyl compound or diazonium salt compound represented by thefollowing formula (7) or (8). ##STR3##

In formula (7), Xa represents a trihaloalkyl group having 1 to 3 carbonatoms; W represents an atom of N, S, Se, P or C; Z represents an atomselected from O, N, S, Se and P; Y represents a nonmetal atomic groupnecessary for forming a ring containing a chromophore, provided that thering formed may contain Xa.

Formula (8)

    Ar--N.sup.+.sub.2 X.sup.-

In formula (8), Ar represents an aryl group, and X⁻ represents a counterion.

Concretely, the trihaloalkyl compound represented bu formula (7)includes a compound represented by formula (9), (10) or (11). ##STR4##

In formulas (9) to (11), Xa represents a trihaloalkyl group having 1 to3 carbon atoms, L represents a hydrogen atom or a methyl group, J anaryl group or heterocyclic group, each of which may be substituted, andn is an integer of 0, 1 or 2.

As examples of the compound represented bu formula (11), are citedbezofuran ring-containing oxadiazole compounds such as the followingcompounds as shown below; ##STR5##2-trichloromethyl-5-(p-methoxystylyl)-1,3,4-oxadiazole compoundsdescribed in JP-A 54-74728;

compounds described in JP-A 60-241049 as shown below; ##STR6## compounddescribed in JP-A 54-74728 as shown below; ##STR7## compounds describedin JP-A 55-77742; ##STR8## compound described in JP-A 60-3626; ##STR9##compound described in JP-A 60-177430; ##STR10## compound described inJP-A 143748. ##STR11##

As examples of the compounds represented by formulas (10) and (11) arecited a 4-(2,4-dimethoy-4-stylyl)-6-trichloromethyl-2-pyrrone compounddescribed in JP-A 53-36223, and a2,4-bis-(trichloromethyl)-6-p-methoxystylyl-s-triazine compound and2,4-bis-(trichloromethyl)-6-p-dimethylaminostylyl-s-triazine compounddescribed in JP-A 48-36281.

With regard to the diazonium compond, is preferble a diazonium compoundcapable of producing a strong Lewis base upon exposure to light. Acounter ion thereof is preferably an inorganic compound ion. As anexample of the compound is cited an aromatic diazonium salt, an anionportion of which is a phosphorus fluoride ion, arsenic fluoride ion,antimony fluoride ion, antimony chloride, tin chloride, bismuth chlorideor zinc chloride ion. A p-diazophenylamine salt is preferable.

The compound capable of forming an acid or radical upon exposure tolight is contained in an amount of 0.01 to 20% by weight, preferably 0.1to 20% by weight and more preferably 0.2 to 10% by weight based on thetotal photosensitive composition.

In combination with the compound capable of forming an acid or radicalupon exposure to light, the photosensitive composition may contain acolor changing agent, which changes color upon reaction with aphotolytic product of the compound. The color changing agent isclassified into two types of color-forming and discoloring orcolor-changing. The discoloring or color-changing type color changingagent includes various dyes such as diphenylmethane dyes,triphenylmethane type thiazine dyes, oxazine dyes, xanthene dyes,anthraquinone dyes, iminonaphthoquinone dyes and azomethine dyes.

As examples thereof are cited Briliant green, Eosin, Ethyl violet,Erythrosin B, Methyl green, Crystal violet, Basic fuchsine,Phenolphthalein, 1,3-diphenyltriazine, Alizarine red S, Thymolphthalein,Methyl violet 2B, Quinadine red, Rose bengale, Metanil yellow,Thymolsulfophthalein, Xylenol blue, Methyl orange, Orange IV,Diphenylthiocarbazone, 2,7-dichloro-fluoresein, Para-methyl red, Congored, Benzopurpurin 4B, α-Naphthyl red, Nile blue 2B, Nile blue A,Phenaphthalene, Methyl violet, Para-fuchsine, Victoria pure blue BOH(product of Hodogaya Kagaku), Oil blue #603 (product of OrientKagakukogyo), Oil pink #312 (product of Orient Kagakukogyo), Oil red 5B(product of Orient Kagakukogyo), Oil scarlet #308 (product of OrientKagakukogyo), Oil red OG (product of Orient kagakukogyo), Oil red RR(product of Orient kagakukogyo), Oil green #502 (product of Orientkagakukogyo), Spiron red BEH special (product of Hodogaya Kagaku),m-Cresol purple, Cresol red, Rhodamine B, Rhodamine 6G, First acidviolet R, Sulforhodamine, Auramine,4-p-diethylaminophenylimino-naphthoquinone,2-carbostearylamino-4-p-dihydroxyethylamino-phenyliminonaphthoquinone,p-methoxybenzoyl-p'-diethylamino-o'-methylphenyliminoacetoanilide,cyano-p-diethylaminophenyliminoacetoanilide,1-phenyl-3-methyl-4-p-diethylaminophenylimino-5-pyrazolone and1-β-naphthyl-4-p-diethylaminophenylimino-5-pyrazolone.

As color forming type color changing agents are cited aryl amines. Thearyl amines include leuco dyes as well as amines such as a primary amineand secondary amine. Examples thereof include diphenylamine,dibenzylaniline, triphenylamine, diethylaniline,diphenyl-p-phenylenediamine, p-toluidine, 4,4'-biphenyldiamine,o-chloroaniline, o-bromoaniline, 4-chloro-0-phenylenediamine,o-brom-N,N-dimethylaniline, 1,2,3-triphenylguanidine, naphthylamine,diaminodiphenylmethane, aniline, 2,5-dichloroaniline,N-methyldiphenylamine, o-toluidine,p,p'-tetramethyldiaminodiphenylmethane, N,N-dimethyl-p-phenylenediamine,1,2-dianilinoethylene, p,p',p"-hexamethyltriaminotriphenylmethane,p,p'-tetramethyldiaminotriphenylmethane,p,p'-tetramethyldiaminodiphenylmethylimine,p,p',p"-triamino-o-methyltriphenylmethane,p,p',p"-triaminotriphenylcarbinol,p,p'-tetramethylaminodiphenyl-4-anilinonaphthylmethane,p,p'p"-triaminotriphenylmethane andp,p'p"-hexapropyltriaminotriphenylmethane.

Among these color changing agents, in the invention, is preferable a dyecapable of being color-changed within a pH range of 1 to 5. Theproportion of the color changing agent contained in the photosensitivecomposition is 0.01 to 10% by weight, preferably 0.02 to 5% by weight.

The photosensitive composition contains preferably a condensation resinof a substituted phenol represented by the following formula (12) and analdehyde, and/or an ester compound of the resin witho-naphthoquinonediazidosulfonic acid.

Foemula (12) ##STR12##

In the formula, R₅ and R₆ each represent a hydrogen atom, alkyl group(including analkyl group having 1 to 3 carbon atom, preferably 1 or 2carbon atoms) or a halogen atom (including fluorine, chlorine, bromineand iodide, preferably chlorine and bromine); R₇ representsan alkylgroup having 2 or more carbon atoms (preferably 15 or less carbon atomsand more preferably 3 to 8 carbon atoms) or a cycloalkyl group(including one having 3 to 8 carbon atoms, more preferably 3 to 8 carbonatoms).

Examples of the substituted phenols include isopropylphenol,tert-butylphenol, tert-amylphenol, hexylphenol, tert-octylphenol,cyclohexylphenol, 3-methyl-4-chloro-5-tert-butylphenol, isopropylcresol,tert-butylcresol, tert-amylcresol, hexylcresol, tert-octylcresol andtert-butylcresol. Among these are preferable tert-octylphenol andtert-butylphenol.

Examples of the aldehyde include aliphatic and aromatic aldehydes suchas formaldehyde, benzaldehyde, acetoaldehyde, acrolein, crotonaldehydeand furfural, including 1 to 6 carbon atoms. Among these are preferableformaldehyde and benzaldehyde.

The condensation resin of the substituted phenol with the aldehyde canbe synthesized by the condensation polymerization of the substitutedphenol represented by formula (12) and the aldehyde in the presence ofan acid catalyst. As the acid catalyst, an inorganic or organic acidsuch as hydrochloric acid, oxalic acid, sulfuric acid or phosphoric acidis usable. The ratio of the substituted phenol to the aldehyde is 0.7 to1.0 mol of the aldehyde per 1 mol of the phenol. As a reaction solvent,for example, an alcohol, aceton, water or tetrahydrofiran is usable. Thereaction is carried out at a given temperature (-5° to 120° C.) and overa period of time (3 to 48 hrs.), subsequently heated under reducedpressure and subjected to water-washing. Thereafter, the product can beobtained by dehydration or precipitation.

The ester compound of the condensation resin of the phenol and aldehydewith an o-naphthoquinonediazidosulfonic acid can be prepared by aprocess comprising dissolving the resin in an appropriate solvent suchas dioxane; adding thereto o-naphthoquinonediazidosufonic acid chloride;and dropwise adding an alkali such as sodium carbonate until reachingthe equivalent point to make esterfication.

In the ester compound, the condensation ratio of theo-naphthoquinonediazidosulfonic acid chloride to a hydroxy group of thephenol (reaction ratio per hydroxy group) is preferably 5 to 80%, morepreferably 20 to 70% and further more preferably 30 to 60%. Thecondensation ratio can be calculated by determining a sulfur atomcontent of sulfonyl groups through elemental analysis.

The condensation resin of the substituted phenol represented by formula(12) and the aldehyde, and the o-naphthoquinonediazidosulfonic acidester of the resin each are contained in amount of 0.05 to 15% byweight, preferably 1 to 10% by weight. The weight-averaged molecularweight (Mw) thereof each are in a range of 5.0×10² to 5.0×10³,preferably 7.0×10² to 3.0×10³. The number-averaged molecular weight (Mn)thereof each are 3.0×10² to 2.5×10³, preferably 4.0×10² to 2.0×10³.

The molecular weights above-described can be measured by a GPC method.The number-averaged molecular weight and weight-averaged molecularweight can be calculated in accordance with the method described in M.Tsuge, T. Miyahashi & S. Tanaka, "Nihon Kagakukaishi" page 800-805,(1972).

The photosensitive composition may further contain a compound having atleast one of the following structure units (D) and (E),

    Structure unit  D!: --(CH.sub.2 CH.sub.2 O).sub.n --

    Structure unit  E!: -- CH.sub.2 CH(CH.sub.3)--O!.sub.n --

(In the formulas, n is an integer of 2 to 5000.)

The compound having at least one of the structure units (D) and (E)includes any one having either or both of the structure units (D) and(E), which have preferably n of 2 to 5000 and a boiling point of 240° C.or higher, more preferably 2 to 500 and 280° C. or higher, andfurthermore preferably n of 3 to 100.

Examples of these compound are cited as follows:

Polyethyleneglycol

    HO--(CH.sub.2 CH.sub.2 O).sub.n --H

Polyoxyethylene alkyl ether

    RO(CH.sub.2 CH.sub.2 O).sub.n --H

Polyoxyethylen alkylphenyl ether ##STR13## Polyoxyethylene polystylenephenyl ether ##STR14## Polyoxyethylen-Polyoxypropylene glycol e.g.,##STR15## (including block polymer and random polymer)Polyoxyethylen-Polyoxypropylene alkyl ether (alkylether is formed at theterminal, including a random polymer) ##STR16## Ethylene oxidederivative of alkylphenol-formalin condensation product ##STR17##Polyoxyethylene-polyhydric alcohol partial ester e.g., ##STR18##Polyoxyethylen-aliphatic acid ester (e.g., RCOO(CH₂ CH₂ O) nHPolyoxyethylenealkylamine ##STR19##

Preferable examples thereof are cited as follows: polyoxyethylene laurylether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether,polyoxyethylene oleyl ether, polyoxyethylene polyhydric alcohol ether,polyoxyethylene octylphenyl ether, polyoxyethylene nonylphenyl ether,polyoxyethylene sorbitan monolauryl ether, polyoxyethylene sorbitanmonopalmitate ether, polyoxyethylene sorbitan monostearate,polyoxyethylene sorbitan tristearate, polyoxyethylenesorbitanmonooleate, tetraoleic acid polyoxyethylene sorbite, polyethylene glycolmonostearate, polyethylene glycol monooleate, polyethylene glycoldistearate, polyoxyethylene nonylphenyl ether-formaldehyde condensationproduct, block polymer of oxyethylene and oxypropylene, polyethyleneglycol and tetraethylene glycol.

The proportion of the compound having the structure unit (D) or (E)contained in the photosensitive composition is preferably 0.1 to 20% byweight, more preferably 0.2 to 10% by weight based on the totalcomposition. The compound may be used singly or in combination thereof.

Further, a colorant such as a dye or pigment, sensitizer, plasicizer orsurfactant may optionally incorporated into the photosensitivecomposition.

These components are dissolved in a solvent as described below andcoated on an appropriate support to provide a photosensitive layer, anda presensitized lithographic printing plate can be obtained.

As solvents used for dissolving components of the photosensitivecomposition afore-described, are cited cellosolves such as methylcellosolve, methyl cellosolve acetate, ethyl cellosolve and ethylcellosolve acetate; dimethylformamide; dimethylsulfoxide; dioxane;acetone; cyclohexane; trichloroethylene and methylethylketone. Thesesolvents may be used singly or in combimation thereof.

The negative-working photosensitive composition includes aphotosensitive composition containing a photosensitive diazo compound, aphotopolymerizing compound or a photocross-linking compound. Thephoto-hardenable, photosensitive composition containing photosensitivediazo compound will be described as follows.

As the photosensitive diazo compound used in the present invention, arepreferably used a diazonium resin which is prepared by condensing anaromatic diazonium salt, in an acidic medium, with an organic condensingagent including aldehydes such as formaldehyde and acetoaldehyde, andacetals. Further, there may be used a condensation copolymer resin of anaromatic diazonium salt and aromatic sulfonic acid (salt) compound withformaldehyde.

The diazonium resin includes, for example, a condensation product ofp-diazodiphenylamine with formaldehyde or acetoaldehyde; a diazoniumresin inorganic salt of an organic solvent-soluble product from aco-condensation product of p-diazodiphenylamine and benzenesulfonic acid(salt) with formaldehyde or acetoaldehyde, and a hexafluorophosphate ortetrafluoroborate; and an organic solvent-soluble diazonium resinorganic acid salt of the above described condensation product, and asulfonic acid such as p-toluenesulfonic acid (or salt), phosphinic acidsuch as benzenephosphinic acid (or salt) or hydroxyl group containingcompound such as 2,4-dihydroxybenzophenone or2-hydroxy-4-methoxybenzophenone-5-sulfonic acid (or salt).

Examples of the diazonium resin include 4-diazodiphenylaminehexafluorophosphate-formaldehyde resin, 4-diazophenylaminehexafluoriphosphate-acetoaldehyde resin, 4-diazo-4'-methoxydiphenylaminetetrafluoroborate-formaldehyde resin, 4-diazo-4'-methoxydiphenylaminetetrafluoroborate-acetoaldehyde resin, benzenesulfonicacid-4-diazodiphenylamine tetrafluoroborate-formaldehyde resin,benzenesulfonic acid-4-diazodiphenylaminetetrafluoroborate-acetoaldehyde resin and 4-diazodiphenylamine2-hydroxy-4-methoxybenzophenone-5-sulfonate-formaldehyde resin.

With respect to the molecular weight of the diazonium resin, it isoptionally variable, depending on a molar ratio of each monomer andcondensation conditions. The molecular weight is feasible in a range of400 to 10000, preferably 800 to 5000. The photosensitive diazonium resinmay be contained, in the photosensitive layer, in an amount of 1 to 60%by weight, preferably 3 to 30% by weight.

The photosensitive diazonium resin used in the present invention is usedpreferably in combination with an alkali-soluble or swellablehydrophobic polymer compound. As the hydrophobic polymer compound, iscited a copolymer comprised of monomers (as a component unit) similar tothose used in the afore-described photosensitive diazonium resin.

The monomers are selected from a compound having anaddition-polymerizable, unsaturated bond including acrylamides,methacrylamides, α,β-unsaturated carboxylic acids, alkyl acrylates,alkyl methacrylates, vinyl ethers, vinyl esters, vinyl ketones, stylenesand olefins.

As examples thereof are cited those as shown in the following (1)through (10);

(1) α,β-unsaturated carboxylic acids such as acrylic acid, methacrylicacid and anhydrous maleic acid;

(2) alkyl acrylates such as methyl acrylate, ethyl acrylate, propylacrylate, butyl acrylate, amyl acrylate, hexyl acrylate, octylyacrylate, chloroethyl acrylate, 2-hydroxyethyl acrylate, glycidylacrylate and N-dimethylaminoethyl acrylate;

(3) alkyl methacrylates such as methyl methacrylate, ethyl methacrylate,propyl methacrylate, butyl methacrylate, amyl methacrylate, cyclohaxylmethacrylate, 2-hyroxyethyl methacrylate, 4-hydroxbutyl methacrylate,glycidyl methacrylate and N-dimethylaminoethyl acrylate;

(4) acrylamides or methacrylamides such as acrylamide, methacrylamide,N-methylolacrylamide, N-methylolmethacrylamide, N-ethylacrylamide,N-hexylmethacrylamide, N-cyclohexylacrylamide, N-hydroxyethylacrylamide,N-phenylacrylamide, N-hydoxyphenylmethacrylamide andN-ethyl-N-phenylacrylamie;

(5) vinyl ethers such as ethylvinyl ether, 2-chloroethylvinyl ether,hydroxyvinylethyl ether, propylvinyl ether, butylvinyl ether, octyvinylether and phenylvinyl ether;

(6) vinyl esters such as vinyl actate, vinyl chloroacetate, vinylbutylate and vinyl benzoate;

(7) stylenes such as α-methylstylene, methylstylene such aschloromethylstylene;

(8)vinyl ketones such as methyvinyl ketone, ethylvinyl ketone,propylvinyl ketone and phenylvinyl ketone;

(9) olefins such as ethylene, propylene, isobutylene, butadiene andisoprene; and

(10) N-vinylpyrrolidone, N-vinylcarbazole, 4-vinylpyridine,acrylonitrile and methacrylonitrile. Furthermore, there is included amonomer capable of polymerizing with a monomer represented by thefollowing formula, ##STR20## (In the formula, R₁₁ represents a hydrogenatom, halogen atom or alkyl group; R₁₂ and R₁₃ each represent a hydrogenatom or alkyl group; R₁₄ represents a carboxyl group, carboxylate group,sulfo group or sulfonate group; p is an integer of 1 to 3; q is aninteger of 0 to 4; and Z represents --O-- or --NH--.) Besides theabove-described resins, a polyvinyl butyral resin, polyurethane resin,polyamide resin. epoxy resin, novorak resin, polyvinyl formal resin,polyester resin polycarbonate resin and natural resins are cited.

As preferable addition-polymerizing, unsaturated compounds, are citedα,β-unsaturated carboxylic acids such as acrylic acid and methacrylicacid; alkyl acrylates and alkyl methacrylate such as methyl acrylate,ethyl acrylate, methyl methacrylate and ethyl methacrylate; acrylonirileand methacryloniriole.

The above copolymer can be obtained by a conventional method, andmolecular weight thereof (measured by GPC) is preferably 10,000 to300,000, more preferably 20,000 to 250,000.

The amount of the hydrophobic polymer compound contained in thephotosensitive composition is preferably 1 to 99% by weight, morepreferably 5 to 95% by weight.

The photosensitive composition may further contain optionally a dye,pigment, coating aid or plasticizer.

Examples of the dye include triphenylmethane dyes, such as Victoria pureblue BOH (product by Hodogaya Kagaku), Oil blue #603 (product by Orientkagaku), Peatent pure blue (product by Sumitomo-mikuni kagaku), Crystalviolet, Brilliant green, Ethyl violet, Methyl green, Basic fuchsine,Malachite green, Oil red, m-Cresol purple, Rhodamine B, Auramine,4-p-Diethylaminophenyliminonaphthoquinone andCyano-p-diethylaminophenylacetoanilide; diphenylmethane dyes; oxazinedyes; xanthane dyes; iminonaphthoquinone dyes; azomethine dyes andanthraquinone dyes.

The dye is contained in the photosensitive composition usually in anamount of 0.5 to 10% by weight, preferabl 1 to 5% by weight.

The coating aid includes alkylethers such as ethylcellulose andmethylcellulose, fluorine-containing surfactants and nonionicsurfactants such as Plulonic L64 (product by Asahi Denka). Theplasticizer which is used for the purpose of providing flexibility andabrasion-proof to the coating layer includes butyl phthalate,polyethylene glycol, tributyl citrate, diethyl phthalate, dihexylphthalate, dioctyl phthalate, 2-ethylhexyl phthalate, tricresylphosphate, tributyl phosphate, trioctyl phosphate, tetrahydrofurfuryloleate and oligomer of acrylic acid or methacrylic acid. An inkreceptivity-increasing agent which is used for enhancing ink receptivityof an image area includes an alcoholic half-ester of stylene-anhydrousmaleic acid copolymer described in JP-A 55-527 (1980). Examples of astabilizer include polyacrylic acid, tartaric acid, phosphoric acid,phosphorous acid and organic acids (acrylic acid, methacrylic acid,citric acid, oxalic acid, benzenesulfonic acid, naphthalenesuofonic acidand 4-methoxy-2-hydroxybenzophenone-5-sulfonic acid). The additionamount of these compounds is preferably 0.01 to 30% by weight.

Among the negative-working photosensitive compositions, those containinga photopolymerizing compound wil be explained as below. Thephotopolymerizing compound refers to a compound containing, within themolecule, at least one ethylenic unsaturated double bond capable ofaddition-polymerization. As examples thereof are cited diethylene glycoldi(metha)acrylate, triethyleneglycol di(metha)acrylate, trimethylolpropane tri(metha)acrylate, pentaerythritol triacrylate, hydroquinonedi(metha)acrylate, pyrogallol triacrylate and2,2'-bis(4-acryloxydiethoxyphenyl)propane. The ethylenic compound iscontained in an amount of 5 to 70% by weight, preferably 10 to 50% byweight, based on the total solid photosensitive composition.

The ethylenic compound is used in combination with an alkali-solubleresin as a binder. This resin is preferably a vinyl copolymer having astructure unit containing a phenolic hydroxy group in the molecule,which has been explained as a resin used in combination with ao-naphthoquinonediazido compound or diazo compound. The vinyl copolymeris contained in an amount of 30 to 70% by weight, preferably 40 to 50%by weight, based on the total solid photosensitive composition. Further,a photopolymerization initiator may be incorporated in thephotosensitive layer. Examples thereof include benzoin, benzoinalkylether, benzophenone, anthraquinone, Michler's ketone,trihalomethyl-s-triazine compound, oxadiazole compound, composite ofbiimidazole and Michler's ketone and composite of thioxanthone and anaromatic tertiary amine.

The photopolymerization initiator used in the present invention iscontained in an amount of 0.5 to 30% by weight, preferably 2 to 10% byweight, based on the total solid photosensitive composition. Thediazonium resin is contained in an amount of 1 to 20% by weight,prefrably 2 to 10% by weight, based on the total solid photosensitivecomposition.

In the present invention, the above-described photosensitive compositionis dissolved in an appropriate solvent including cellosolves such asmethyl cellosolve, ethyl cellosolve, methyl cellosolve acetate and ethylcellosolve acetate, methylethyl ketone, ethyl acetate, benzyl alcohol,diacetone alcohol, dimethylformaldehyde, dimethylsulfoxide, dioxane,acetone, cyclohexane and trichloroethylene to obtain a photosensitivesolution. This solution is coated on a support and dried to obtain apresensitized lithographic printing plate.

Coating is made by methods known in the art such as rotary coating,wire-bar coating, dip-coating, air-knife coating, roller coating, bladecoating and curtain coating. The coating amount is, depending on the usethereof, preferably 0.15 to 10 g as solid per m² of the presensitizedlithographic printing plate.

The ablatable light-shielding layer provided in the presensitizedlithographic printing plate of the present invention has to havecapabilities of absorbing light having a first wavelength such as laser,absorbing a light having a second wavelength to which the photosensitivelayer responds and being dissolved-out in a developer with a nonimagearea of the photosensitive layer.

To satisfy these capabilities, the light-shielding layer preferablycontains a water-soluble or aqueous alkali-soluble resin as a maincomponent. The water-soluble resin refers to a polymer compound having asolubility in water of not less than 1 g per 100 g of water. The word,"aqueous alkali-soluble" refers to a solubility in an aqueous alkalinesolution having a pH of 7 to 14 being not less than 1 g per 100 g of thesolution.

Examples of the water-soluble resin include gelatin, polyvinyl alcohol,water-soluble polyvinyl formal, water-soluble polyvinyl acetal,water-soluble polyvinyl butyral, polyvinyl pyrroridone, water-solublepolyester, water-soluble nylon, polyacrylic acid, water-solublepolyurethane, methyl cellulose and hyroxypropyl cellulose. There may beused a copolymer containing a monomer constituting the above-describedresins. Further, as the water-soluble resin is usable an ionomer resinand an ionic bond-containing resin which comprises, as a co-polymerisingcomponent, a sulfo-substituted stylene, acrylic acid, methacrylic acidor anhydrous phthalic acid and further contains a counter ion such asNa⁺, K⁺, Ca⁺, Zn⁺ or NH₄ ⁺. These resin is preferably contained in anamount of 20 to 80% by weight, based on the light-shielding layer.

As the aqueous alkali-soluble resin, there are usable various kinds ofresins known in the art, and particularly, novolak resin and vinylpolymer having a structure unit containing a phenolic hydroxyl group arepreferable. As examples thereof are cited the same ones as described inthe explanation of the photosensitive layer.

The light-shielding layer preferably contains a near-infrared absorbingdye for absorbing high intensity laser light. As the near infraredabsorbing dye, particularly in the case when exposed to the laser lighthaving a wavelength in a range of red to near-infrared, there can beused dyes described in Japanese Patent Application No. 4-334584 (1992),page 7, and further cyanine dyes, squalinium dyes, croconium dyes,azulenium dyes, phthalocyanine dyes, naphthalocyanine dyes,anthraquinone dyes, dithiol metal complex dyes, indoaniline metalcomplex dyes, intermolecular charge transfer complex dyes, transitionmetal complex dyes and aluminum diinmonium dyes selected from thenear-infrared dyes described in "Kinozairyo (Functional materials)",June, 1990, pages 64-68 and dyes used for photo-recording described in"Shikizai (Color materials)" Vol. 61, page 218-223 (1988).

In the case where the light-shielding layer contains the water-solubleresin, the light absorbing material is also preferably water-soluble andmore preferably, a tricarbocyanine dye having a water-soubilizing groupsuch as a sulfo group.

In the case of the light-shielding layer containing the water-solubleresin, a water-soluble near-infrared absorptive dye is preferably usedas a light-heat converting substance which plays a role in convertinglight into heat. The water-soluble near-infrared absorptive dye haspreferably an acid group such as a sulfo group, carboxyl group orphosphono group, more preferably a sulfo group. The water-solublenear-infrared absorbing dye is preferably one represented by thefollowing formulas (13) and (24).

Formula (13) ##STR21##

Formula (14) ##STR22##

In formulas (13) and (14), Z₁ and Z₂ each represent an atomic groupnecessary to form a substituted or unsubstituted pyridine ring, asubstituted or unsubstituted quinoline ring, a substituted orunsubstituted benzene ring or a substituted or unsubstituted naphthalenering; (a ═N⁺ (R₁)-- bond or a --N(R₆)-- bond may be contained in Z₁ orZ₂ when Z₁ or Z₂ represents a pyridine ring or a quinoline ring).

Z₃ and Z₄ each represent an atomic group necessary to form a substitutedor unsubstituted quinoline ring or a substituted or unsubstitutedpyridine ring, and may contain in the ring of Z₃ and Z₄ a ═N⁺ (R₁)--bond or a --N(R₆)-- bond.

Y₁ and Y₂ each represent a dialkyl-substituted carbon atom, a vinylenegroup, an oxygen, sulfur or selenium atom, or a nitrogen atom bondedwith a substituted or unsubstituted alkyl or aryl group.

R₁ and R₆ each represent a substituted or unsubstituted alkyl group; R₂,R₄ and R₅ each represent a hydrogen atom, a substituted or unsubstitutedalkyl group; R₃ represents a hydrogen atom, a halogen atom, asubstituted or unsubstituted alkyl group, or a substituted orunsubstituted aryl group or a nitrogen atom bonded with an alkyl or arylgroup.

But at least one of the groups represented by Z₁ to Z₄ and R₁ to R₆ issubstituted by at least one of sulfo, carboxyl and phosphono groups(preferably sulfo group).

X⁻ represents an anion; m represents 0 or 1; n represents an integer of1 or 2, provided that n is 1 when the dye forms an inner salt.

Formula (15) ##STR23##

In the formula, R₁, R₂, R₃ and R₄ each represent a substituted orunsubstituted alkyl group, --N(R₅)(R₆), ═N⁺ (R₅)(R₆) or a sulfo group;R₅ and R₆ each represent a substituted or unsubstituted alkyl group,provided that at least one of the groups represented by R₁ to R₆ issubstituted by at least one of sulfo, carboxyl and phosphono groups(preferably sulfo group); X⁻ represents an anion.

Formula (16) ##STR24##

In the formula, R₁, R₂, R₃ and R₄ each represent a substituted orunsubstituted alkyl group, and at least one of them is substituted by atleast one of the acid groups of sulfo, carboxyl and phosphono groups(preferably sulfo group).

Formula (17) ##STR25##

In the formula, R₁ and R₂ each represent a substituted or unsubstitutedalkyl group, at least one of which is substituted by at least one of theacid groups of sulfo, carboxyl and phosphono groups (preferably sulfogroup); R₃ and R₄ each represent a hydrogen atom or an alkyl group whichmay be substituted by one of the acid groups of sulfo, carboxyl andphosphono groups (preferably sulfo group).

Formula (18) ##STR26##

In the formula, R₁, R₂ and R₃ each represent a substituted orunsubstituted alkyl group, at least one of which is substituted by atleast one of the acid groups of sulfo, carboxyl and phosphonogroups(preferably sulfo group); X⁻ represents an anion.

Formula (19) ##STR27##

In the formula, R₁ and R₂ each represent a sulfo, carboxyl or phosphonogroup, or an alkyl or aryl group substituted with one of such acidgroups.

Formula (20) ##STR28##

In the formula, R₁ represents a hydrogen atom, an amido, amino, alkyl,sulfo, carboxyl or phosphono group, or an alkyl group substituted by oneof such groups; R₂ and R₃ each represent an alkyl group or an alkylgroup substituted by at least one of sulfo, carboxyl and phosphonogroups; R₄ represents a hydrogen atom, a sulfo, carboxyl or phosphonogroup, or an alkyl group substituted by one of these groups; Mrepresents a metal atom (preferably Cu or Ni); X⁻ represents an anion.

Formula (21) ##STR29##

In the formula, R₁ represents a hydrogen atom or an alkyl groupsubstituted by one of sulfo, carboxyl and phosphono groups; R₂represents an alkyl, amido, nitro, sulfo, carboxyl or phosphono group.

Formula (22) ##STR30##

In the formula, R₁ and R₂ each represent a sulfo, carboxyl or phosphonogroup or an alkyl group substituted by one of these groups; n represents2 or 3; R₃, R₄, R₅ and R₆, which may be the same or different, eachrepresent an alkyl group.

Formula (23) ##STR31##

In the formula, R₁ and R₂ each represent a hydrogen atom, a sulfo,carboxyl or phosphono group or an alkyl group substituted by one ofthem, provided that R₁ and R₂ are not hydrogen atoms concurrently; Mrepresents a divalent or trivalent metal atom; n represents an integerof 2 or 3.

Formula (24) ##STR32##

In the formula, R₁, R₂, R₃ and R₄ each represent a hydrogen, a sulfo,carboxyl or phosphono group or an alkyl group substituted by one ofthem, provided that all of R₁ to R₄ are not hydrogen atoms concurrently;M represents a divalent metal atom.

Typical examples of the compounds represented by formulas (13) to (24)are as follows but not limited to them. ##STR33##

There may be usable near infrared sbsorbing dyes described in JP-A62-123454 (1987) and 3-146565 (1991). In formulas (13) to (24), there ispreferably used a dye which has a substituent including a sulfo group,carboxyl group and phosphono group.

Among these dyes, those which are soluble in an organic solvent may bedispersed, with a high boiling solvent, in the water-soluble resin ascolloidal particles. An organic pigment which is insoluble in water andan organic solvent may be dispersed in the water-soluble resin by usingan appropriate dispersing agent or surfactant. As the dispersing agentand surfactant, there can be used materials known in the art.

Examples thereof include an alkylamine phosphate, alkylpyridiniumchloride, alkylpolyether sulfate, alkylallylsulfonate,alkylbenzenesulfonate, alkylnaphthalenesulfonate,alkylphenolpolyethylene ether, condensate of allylsulfonic acid, higheralcohol sulfonic acid sodium salt, dialkylsulfosuccinate, sulfuric acidester of an aliphatic acid amide derivative, hydrophobic polyester,cellulose glycolsorbitanmonostearate, cetylalcohol sulfuric acid estersodium salt, sorbitan alkylate, sorbitan ester quaternary ammonium salt,trimethylstearylammonium chloride, naphthalenesulfonic acid condensate,naphthalene-formalin condensate dinaphthylmetasulfonate, sulfonatedcaster oil, bisnaphthalenesulfonate, polyoxyethylene alkyl ether,polyoxyethylene alkylallyl ether, polyoxyethylene sorbitanalkyl ether,polyoxyethylene alkylamide, polyoxyethylene alkylamine, polyethyleneglycol oleyl ether, polyethylene glycol ester, polyethylene glycolalkylallyl ether sodium sulfonate and polyethylene alkylphenol ether.Furthermore, as more conctrete examples, are cited sodium oleate, sodiumrosinate, sodium lauryl sulfate, sodium alkylmonoglyceride sulfate,sodium dodecylbenzenesulfonate, sodium isopropylnaphthalene-sulfonate,sodium monobutylphenylphenoldisulfonate, sodium dibutylphenylphenoldisulfonate, sodium diisobutylsulfo-succinate, sodiumpetroleum hydrocarbon sulfonate, turkey red oil, zinc naphthenate,cupper oleate, ammonium alkylbenzenesulfonate, petroleum alkylsulfuricacid ester, sodium dioctylsulfosuccinate, triethanolamine oleic acidsoap, sodium dinaphthylmethanesulfonate, sorbitan monolaurate, sorbitantrioleate, polyoxyethylene sorbitan monooleate, polyoxyethylene glycoldioleate, pentaerythritol monooleate, sorbitan sesquioleate,polyoxyethylene oleylphosphate, lecithin, ethylenediamine, triethyamineand triethanolamine.

As a method for dipersing an oil-soluble dye in the water-soluble resin,there can be applied various methods including an aqueous alkalinesolution dispersion method, solid dispersion method, latex dispersionmethod and oil-in-water type emulsion-dispersing method. These can beoptionally used in accordance with the chemical structure of theoil-soluble dye. In the present invention, the oil-in-water typeemulsion dispersing method, solid particle dispersion method and latexdispersion method are particularly effective. The methods have beenknown in the art. With regard to the oil-in-water dispersion method,there can be applied a method known as a technique for dispersing ahydrophobic material such as a photographic coupler, as described inJP-A 59-109055. For example, it is conducted in such a manner that theoil soluble dye is dissolved in a high boiling solvent such asN-n-butylacetianilide, diethyllauramide, dibutylphthalate, tricresylphosphate or N-dodecylpyrrolidone and finely dispersed in a hydrophiliccolloid such as gelatin.

The dye is dissolved in a high boiling solvent havin a boiling point of175° C. or more, which is optionally used in combination with a lowboiling solvent and finely dispersed in an aqueous solution of ahydrophilic binder such as gelatin with the use of a surfactant. Theresulting dispersion is incorporated in a hydrophilic colloidal layer.As the high boiling solvent are usable organic acid amides; carbamates;esters; ketones; urea derivatives; specifically, phthalic acid esterssuch as dimethyl phthalate, diethyl phthalate, dipropyl phthalate,dibutyl phthalate, di-n-octyl phthalate, diisooctyl phthalate, diamylphthalate, dinonyl phthalate and diisodecyl phthalate; phosphoric acidesters such as tricresyl phosphate, triphenyl phosphate,tri-(2-ethylhexyl) phosphate and triisononyl phosphate; sebacic acidesters such as diocty cebacate and di-(2-ethylhexy cebacate; glycerinesters such as glycerol tripropionate and glycerol tributylate; estersof adipic acid, glutaric acid, maleic acid fumaric acid and citric acid.The oil soluble dye is also dissolved in the high boiling solvent and alow boiling solvent optionally selected from methyl acetate, ethylacetate, propyl acetate, butyl acetate, butyl propionate, cyclohexanol,cyclohexane, tetrahydrofuran, methyl alcohol, ethyl alcohol,acetonitrile, dimethylformamide, dioxane, methylethylketone,methylisobutylketone, diethylketone, diethylene glycol monoacetate,acetylacetone, nitromethane, carbon tetrachloride, and chloroform (thesehigh boiling or low boiling solvents are used singly or in combinationthereof); the resulting solution is mixed with an aqueous solutioncontaining a hydrophilic binder such as gelatin which further containsan anionic surfactant such as alkylbenzenesulfonic acid oralkylnaphthalenesulfonic acid and/or a nonionic surfactant such assorbitan sesquioleic acid ester or sorbitan monolauric acid ester anddispersed with the use of a high-speed mixer, colloid mill or ultrasonicdispersion machine to obtain an emulsified dispersion, which may beincorporated in a hydrophilic colloid.

With regard to the solid particle dispersion method, there can beapplied a technique as described in JP-A 3-296045. The solid dispersionmethod includes a precipitation method and mechanical grinding method.As the precipitation method, there are available a method in which theoil soluble dye is dissolved in an organic solvent and added in water tobe dispersed, and a method in which the dye is dissolved in awater-inmiscible, low boiling solvent to form a oil-in-water dispersionand then the solvent is removed by evaporation. With regard to themechanical grinding method, there is availble a method in which the oilsoluble dye is reduced to fine powder by means of high energy such asultrasonic and the powder is dispersed in a hydrophilic colloid and amethod in which the dye is wetted, in the presence of a dispersingagent, with water or poor solvent and then dispersed in the form of fineparticles using a mill. As a apparatus for performing the soilidparticle dispersion used in the present invention, ball mill, roll milland sand mill are available. Among these is preferable the sand mill,which is commercially available.

Materials employed as a medium in the mill include glass, alumina,zirconia, agate, stainless and nylon. Among these, are preferable glass,zirconia and alumina. The glass contains preferably silicon dioxide inan amount of not less than 60% by weight. The medium is preferablysphere, having a particle size of 0.1 to 20 mm, preferably 0.5 to 5 mmin diameter. As an example of the glass medium is cited Bright glassbeads (product by Bright Kogyo Co., Ltd.).

The latex dispersion method is referred to JP-A 49-74538, 51-59943,54-32552 and Reaearch Disclosure No. 14850 page 77-79 (Aug., 1976).

The ablatable light-shielding layer of the presensitized lithographicprinting plate of the present invention contains the near-infraredabsorbing dye preferably in an amount of 1 to 50% by weight. Thenear-infrared absorbing dye may be in more amounts, unless lowered inthe shielding ability of the light-shielding layer.

The light-shielding layer preferably contains a substance capable ofabsorbing light in a wavelength range, to which the photosensitive layerresponds photochemically. Thus, the substance is capable of absorbingthe second wavelength. The substance is selected optionally inaccordance with the photosensitive layer. The photosensitive wavelengthof the diazonium resin or naphthoquinone photosensitive material is in arange of 300 to 500 nm. As substancess capable of absorbing the light inthis range, are cited inorganic pigments such as carbon black, cadmiumyellow, cadmium red titanium yellow, chrome yellow, zinc yellow, bariumchromate, yellow iron oxide and red iron oxide; organic pigments such ashanza yellow and hanza yellow 10G; water-soluble dye such as tartrazine;benzotriazole UV-absorbents such as 2-(2-hydroxyphenyl)bezotriazole;benzophenone UV absorbent such as 2, 4-hydroxybenzophenone and metalfine particles dispersion dispersed in water in a colloidal form colloidsuch as coloidal silver, cadmium yellow, cadmium red titanium yellow,chrome yellow, zinc yellow, barium chromate, yellow iron oxide and rediron oxide; organic pigments such as hanza yellow and hanza yellow 10G;water-soluble dye such as tartrazine; benzotriazole UV-absorbents suchas 2-(2-hydroxyphenyl)bezotriazole; benzophenone UV absorbent such as2,4-hydroxybenzophenone and metal fine particles dispersion dispersedinwater in a colloidal form colloid such as coloidal silver.

Since a water soluble resin is used in the light-shielding layer, if thesubstance capable of absorbing light having a photosensitive wavelengthof the photosensitive layer is water soluble, a coating solution can bereadily prepared. However, a material which is oil-soluble or insolublein water and solvent may be dispersed in the water-soluble resin in amanner similar to the case of the near-infrared absorptive dyesafore-described.

The substance capable of absorbing the photosensitive wavelength of thephotosensitive layer may be used singly or in combination thereof. Theproportion of the substance capable of absorbing the photosensitivewavelength of the photosensitive layer contained in the light-shieldinglayer is preferably 5 to 60% by weight. It is preferable to adjust atransmission density of the light-shielding layer so as to have adensity of 2 or more at the centered wavelength of the photosensitivewavelengths.

The light-shielding layer may further contain a coating aid such as asurfactant, an antistatic agent such as a conductive compound or ananti-blocking agent such as a mold lublicant or matting agent.

The thickness of the light-shielding layer is preferably as thinner aspossible. It is preferably in a range of 0.1 to 2.0 μm, more preferably0.1 to 1.0 μm. If high intensity exposure is made, a thick layer may beablatable so that the thickness is not necessarily limited to theabove-value.

The light-shielding layer may be comprised of plural layers havingdifferent functions. As the function is cited light-shielding ability,light absorptivity and anti-blocking property. These functions can beshared with plural layers. The light-shielding layer can be coated in amanner similar to the case of the photosensitive layer.

In the present invention, another layer may be provided in addition tothe photosensitive layer and ablatable light-shielding layer. A subbinglayer, for example, may be provided between the support andphotosensitive layer so as to enhance adhesive property. A backing layermay be provided on the backing side of the support for the purpose ofproviding transporting stability and antiabration. The thickness of thebacking layer is preferably 0.1 to 1 μm.

An interlayer may be provided between the photosensitive layer andlight-shielding layer.

The interlayer has desirably such charactristics that (i) it istransparent to the photosensitive wavelength range of the photosensitivelayer; (ii) soluble or capable of being swollen in water or aqueousalkaline solution; and (iii) prevents the high intensitylight-absorptive material or photosensitive wavelength-absorptivematerial from diffusive migration to an adjacent layer during or aftermanufacturing.

To satisfy the above-described requirements, the interlayer ispreferably comprised of the following polymer binder. Thus, in the casewhere a binder contained in the light-shielding layer provided on theinterlayer is a water-soluble resin, the interlayer is mainly comprisedpreferably of a hydrophobic resin soluble in an aqueous alkalinesolution. In the case when the binder is a hydrophobic resin soluble inan aqueous alkaline solution, on the other hand, the interlayer ismainly comprised preferably of a water soluble resin.

As examples of the water soluble resin and hydrophobic resin soluble inan aqueous alkaline solution are cited the same resins as used in thelight-shielding layer afore-described.

The thickness of the interlayer is preferably 0.1 to 10 μm, morepreferably 0.5 to 5 mm.

The ablatable light-shielding layer of the present invention may beseparated into a light-heat converting layer and a light-shieldinglayer.

With respect to the case where the ablatable light-shielding layer iscomprised of a light-heat converting layer and a light-shielding layer,it will be explained as below.

The light-heat converting layer is characterized in that it absorbs atleast 80% of the light having a first wavelength of 500 nm or more. Theabsorbed wavelength is preferably in a range of 700 to 1200 nm and theabsorption ratio is preferably 90% or more. The thickness of the layeris 1 mm or less, more preferably 0.01 to 0.5 mm.

The light-heat converting layer itself is not necessarily destroyed bylaser light. Even if the light-heat converting layer is still remained,it is preferable that an ultraviolet radiation (thus, light having asecond wavelength) reaches a lower photosensitive layer. Accordingly,the absorption ratio of the light-heat converting layer is preferablyless than 30% with respect to the light having the second wavelength.

The light-heat converting layer is formed by mixing a water solubleresin and a dye (preferably, infrared-absorbing dye), and coating themixture on the photosensitive layer. Therefore,the composition of thecoating solution is preferably one which does not dissolve the lowerlayer during coating.

The infrared absorbing dye used in the present invention refers to thedye having a molar absorption coefficient of 10,000 or more in anappropriate medium with respect to a light having a wavelength in arange of 700 to 1200 nm (visible light or infrared light). The infraredabsorbing dye is contained preferably in an amount of 10% by weight.

In the case where the first wavelength for ablating exposure is in avisible light region, there can be used various kinds of pigments anddyes which are capable of absorbing the exposing light wavelength. Inthe case where the first wavelength is in a range of red tonear-infrared, dyes described in Japanese Patent Application 4-334584 atpage 7 and carbon black are usable. There are also usable cyanine dyes,squalinium dyes, croconium dyes, azulenium dyes, phthalocyanine dyes,naphthalocyanine dyes, anthraquinone dyes, dithiol metal complex dyes,indoaniline metal complex dyes, intermolecular charge transfer complexdyes, transition metal complex dyes and aluminum diinmonium dyesselected from the near-infrared dyes described in "Kinozairyo(Functional materials)", June, 1990, pages 64-68 and dyes used forphoto-recording described in "Shikizai (Color materials)" Vol. 61, page218-223 (1988).

The water soluble resin is preferably used in the light-heat convertinglayer so that the dye is preferably water soluble, particularlypreferably a tricarbocyanine dye a water-solubilizing substituent suchas a sulfo group. The water soluble, infrared-absorbing dye preferablyhas an acid group such as a sulfo group (--SO₃ H), carboxy group(--COOH) or phosphono group (--PO₃ H₂), more preferably a sulfono group.The word, "water soluble" refers to "being soluble in water at 25° C. inan amount of 1% or more".

The light-shielding layer has preferably an absorption ratio of 97% ormore, more preferably 99% or more with respect to the second wavelengthof less than 500 nm, so that a UV-absorbing dye is preferably containedin an amount of 10% by weight or more. The dye is optionally selected inaccordance with the photosensitive layer. The photosensitive wavelengthof the photosensitive diazo resin or naphthoquinone is in a range of 300to 500 nm so that, as materials capable of absorbing the light in thiswavelength range, are cited cadmium yellow, cadmium red, titaniumyellow, chrome yellow, zinc yellow, barium chromate, yellow iron oxideand red iron oxide; organic pigments such as hanza yellow and hanzayellow 10G; water-soluble dye such as tartrazine; benzotriazoleUV-absorbents such as 2-(2-hydroxyphenyl)bezotriazole; benzophenone UVabsorbent such as 2,4-hydroxybenzophenone and metal fine particlesdispersion dispersed in water in a colloidal form such as coloidasilver.

In the case where the heat-generating position is located at a lowerportion of the light-shielding layer, the absorbing ratio of the layerwith respect to the light having the first wavelength is preferablysmaller, concretely 30% or less.

Next, a method for preparing a lithographic printing plate of thepresent invention will be explained, based on the drawings. FIG. 1 isschematic illustrations showing a process of preparing the lithographicprinting plate by using a presensitized lithographic printing plate.FIG. 1(a) shows the structure of the presensitized lithographic printingplate, in which 2 is an aluminum support; 3, grains provided on thesurface of the support 2; 4, a negative-workingphotosensitive layercoated on the grains 3; and 5, an ablatable light-shielding layer coatedon the photosensitive layer 4. When, as shown in FIG. 1(b), thepresensitized plate is exposed to laser light 6 from the side of thelight-shielding layer, the light-shielding layer 5 is imagewise ablated,as shown in FIG. 1(c). Subsequently, the presensitized plate is exposedoverall to actinic ray 7 responsive to the photosensitive layer 4 tomake a portion of the photosensitive layer 4 which has been removed byablation, insoluble in a developer. Then, as shown in FIG. 1(d), anotherportion of the photosensitive layer which is soluble in the developer isremoved. In case of a positive-working photosensitive layer, afterexposed to the laser light and the actinic ray, a portion of thephotosensitive layer which has been ablatively removed by thelaser-exposure is made soluble in the developer. Thereafter, the portionof the photosensitive layer which has been laser-exposed is dissolvedout in the developer during development and the light-shielding layerlaser-unexposed is also dissolved out, so that only a laser-unexposedportion of the photosensitive layer is remained on the support to obtainan imagewise formed lithographic printing plate.

Thus, an imaging proces of the invention comprises a step of exposing,to a high intensity light, the side of a ablatable light-shielding layerof a recording material to ablate imagewise the light-shielding layerand a step of exposing the ablated recording material overall to anactinic ray and a step of liquid-developing.

As a laser light source for high intensity exposure, are available asemiconductor laser, He-Ne laser, Ar laser. YAG laser and CO₂ laser. Thesemiconductor laser is preferable in view of handling.

An exposure power density in the focal surface is preferably 100000W/cm² or more, more preferably 200000 w/cm². At a lesser power density,the ablatable light-shielding layer is often not ablated effectively. Anexposing speed is preferably 0.4 m/sec. or more, further preferably 1m/sec. or less. At a slower exposing speed, another layer, besides thelight-shielding layer, may be affected.

Examples of preferable exposure condition are shown as below, but thepresent invention is not limited thereto.

    ______________________________________    Output   Optical Effi-                         Exposing spot                                    Focal surface    power (mW)             ciency (%)  Diameter (μm)                                    power (W/cm.sup.2)    ______________________________________    100      50           6         177000    150      70          10         134000    500      50          10         318000    2000     30          10         764000    ______________________________________

Holes formed by high intensity exposure may be in a dot form or linkedholes. In this case, the image is formed in accordance with the form ofablated holes of the light-shielding layer to become dots or solid. Inthe case of the dot, the more is the number of the dots, higher is animage density. (The image density is proportional to the number of thedots.)

The presensitized lithographic printing plate of the present inventioncomprises the photosensitive layer provided thereon with the ablatablelight-shielding layer so that the presensitized plate is superior instorage stability and it is not needed to work under safe light.

With regard to the actinic ray source for exposing overall thepresensitized plate in which the light-shielding layer has beenimagewise ablated, it is preferable that a light source has a spectralenergy distribution in response to the spectral sensitivity of thephotosensitive layer. A high pressure or ultra-high pressure mercurylamp and metahalide lamp are well suited for the diazonium resin ornaphthoquinone photosensitive material.

In the method for preparing the lithographic printing plate of theinvnetion, the use of laser light for ablating the light-shielding layerenables high definition recording. Accurate reproduction of continuoustone of an image can be made in such a manner that an image density toneis reproduced by controlling thermal energy. The use of a dot-generatotenables to provide thermal energy in response to the dot area.

Next, an exposure unit for a presensitized lithographic printing plateof the invention will be explained as follows, referring to thedrawings. FIG. 2 is a cross-sectional view showing an example of theexposure unit for a presensitized lithographic printing plate of theinvention. The numeral 12 is an enclosure having therein the exposureunit, and 13 is a feeding means for presensitized lithographic printingplate P. The feeding means 13 is so arranged as to feed out pluralpresensitized lithographic printing plates P stacked thereon in a waythat an unillustrated mechanism feeds out constantly the uppermostpresensitized plate successively toward the left-hand side in thefigure. The numeral 14 is a conveyance roller that conveys to holdingmeans 15 the presensitized lithographic printing plates P fed out by thefeeding means 13. The holding means 15 is mainly composed of holdingmember 16, presensitized plate mounting means 17, pressure roll 18,presensitized plate ejecting means 19 and an unillustratedpressure-reducing means.

The holding member 16 is mainly composed of a hollow cylinder which canbe rotated on its rotation axle of rotary shaft 16b at a predeterminedspeed of revolution by an unillustrated mechanism, and an externalcircumferential surface of the hollow cylinder serves as a holdingsurface 16a for holding presensitized lithographic printing plate P. Theholding surface 16a is provided with evacuation holes 22 composed of agreat number of slotted holes located at regular intervals eachpenetrating into the inside of the hollow cylinder, the inside of thehollow cylinder is decompressed by an unillustrated pressure-reducingmeans, and thereby the presensitized lithographic printing plate P canbe sucked through the evacuation holes 22 to be held on the holdingsurface 16a.

The presensitized plate mounting means 17 is one which sandwiches thepresensitized lithographic printing plate P conveyed to a prescribedposition on the holding member 16 by conveyance roller 14, betweenitself and the holding surface 16a.

It sandwiches the leading edge of the presensitized lithographicprinting plate P conveyed by the conveyance roller 14 while beingsupported by an arm (not shown) whose rotation axle is rotary shaft 16bso that the presensitized lithographic printing plate P can be woundaround the holding surface 16a by the rotation of the holding member 16and the arm in the direction of arrow A. Pressure roll 18 is so arrangedas to rotate freely on its rotation axle of rotary shaft 18a and to urgethe holding surface 16a with appropriate force at a predetermined timingby means of an unillustrated control system. When the leading edge ofthe presensitized lithographic printing plate P is sandwiched betweenthe holding surface 16a and the presensitized plate mounting means 17,decompression is started, then the presensitized lithographic printingplate P is sucked through evacuation holes 22, and it is wound aroundthe holding surface 16a to be held thereon when the holding member 16rotates. The pressure roll 18 is urged against the holding surface 16ato bring the presensitized lithographic printing plate P in pressurecontact with the holding surface 16a, and when the full surface of thepresensitized lithographic printing plate P is held on the holdingsurface 16a, the pressure roll 18 leaves the holding surface 16a.Presensitized plate ejecting means 19 sandwiches the trailing edge ofthe presensitized lithographic printing plate P released from suctioncaused by decompression of holding member 16 and transports it toejection portion 26. The numeral 23 represents an optical writing meanswhich is a means for conducting selectively highly intensive exposure onthe presensitized lithographic printing plate P in accordance with imageinformation, and it is structured so that exposure is conducted inaccordance with image information, being controlled by an unillustratedcontrol system known widely. The numeral 25 represents full surfaceirradiation means that irradiates on an entire plane the active lightwhich causes light response on a light-sensitive layer of thepresensitized lithographic printing plate P. The presensitizedlithographic printing plate P on which full surface irradiation isfinished is caught by its trailing edge by the presensitized plateejecting means 19 to be transported to ejection portion 26 where aconveyance means constituting the ejection portion 26 ejects thepresensitized lithographic printing plate P out of enclosure 12.

Next, operations of an exposure unit shown in FIG. 2 will be explainedas follows.

When the uppermost sheet among a plurality of presensitized lithographicprinting plates P stacked on feeding means 13 is fed out toward the leftside in the figure by an unillustrated mechanism, the sheet is conveyedto holding means 15 by conveyance roller 14. When the leading edge ofthe presensitized lithographic printing plate P comes in contact withpresensitized plate mounting means 17, the presensitized plate mountingmeans 17 is urged against holding surface 16a, thereby the leading edgeportion of the presensitized lithographic printing plate P is sandwichedby the presensitized plate mounting means 17, and concurrently withthat, the pressure-reducing means operates and the inside of holdingmember 16 is decompressed and the holding member 16 is rotated in thedirection of arrow A. Next, pressure roll 18 is urged toward holdingsurface 16a to bring presensitized lithographic printing plate P inpressure contact with the holding surface 16a, thus the presensitizedlithographic printing plate P is wound around the holding surface 16a.When the full surface of the presensitized lithographic printing plate Pis held on the holding surface 16a, the pressure roll 18 leaves theholding surface 16a, then, holding member 16 starts rotating at highspeed while holding the presensitized lithographic printing plate P onthe holding surface 16a, exposure is conducted by optical writing means24 in accordance with image information controlled by an unillustratedcontrol mechanism. After imagewise exposure is completed, the fullsurface of the presensitized lithographic printing plate P is exposed toactive light which causes light response on a light-sensitive layer ofthe presensitized lithographic printing plate P by means 25 whichirradiates on the full surface the active light which causes lightresponse on a light-sensitive layer of the presensitized lithographicprinting plate P. After the exposure on the full surface is completed,decompression of holding member 16 is released, then, the trailing edgeof the sheet is sandwiched by presensitized plate ejecting means 19 andthereby the presensitized lithographic printing plate P is conveyed toejection portion 26 by the rotation in the direction of arrow A of boththe presensitized plate 19 and the holding member 16 to be ejected outof enclosure 12.

An optical writing means and a means for irradiation on the full surfacemay also be provided inside a cylindrical holding member. A sectionalview of an example of such exposure unit is shown in FIG. 3. In FIG. 3,the numeral 31 is a holding means for presensitized lithographicprinting plate P, and the holding means 31 is mainly composed of holdingmember 32, presensitized plate mounting means 34 for mountingpresensitized lithographic printing plate P on holding surface 32a ofthe holding member 32, pressure roll 35 and pressure-reducing means (notshown). The holding member 32 is a holding member for presensitizedlithographic printing plate P whose semicylindrical internal surfaceconstitutes holding surface 32a that holds presensitized lithographicprinting plate P, the numeral 33 is an evacuation hole provided on theholding member 32, and presensitized lithographic printing plate P onthe holding surface 32a is sucked through the evacuation hole by anunillustrated pressure-reducing means so that the presensitizedlithographic printing plate P comes in pressure contact with the holdingsurface 32a. The numeral 34 is a presensitized plate mounting meanswhich fixes presensitized lithographic printing plate P on the holdingsurface 32a, and it is provided at an end portion of a swing of an arm(not shown) whose rotation axle is a center line of semicylindricalsurface forming the holding surface 32a, thus, the leading edge of thepresensitized lithographic printing plate P conveyed by conveyanceroller 14 is sandwiched and the presensitized lithographic printingplate P is rotated up to its top portion along the holding surface 32aby the clockwise rotation of the arm. The numeral 35 is a pressure rollthat is arranged to be freely rotatable on its axle of rotary shaft 35a.The rotary shaft 35a is fixed on an arm (not shown) whose rotation axleis a center line of a semicylindrical surface of holding surface 32a,and when the arm rotates, the pressure roll 35 moves along the holdingsurface 32a while applying pressure on the holding surface 32a. Thenumeral 37 is an optical writing means which is arranged to conductsub-scanning in the direction perpendicular to the figure plane and toconduct main scanning on the holding surface 32a in the verticaldirection on the figure, so that images are exposed. The numeral 38 is ameans for irradiating on the full surface, 39 is a sensitized plateejecting means, and after completion of irradiation on the full surface,decompression of holding member is released, and presensitizedlithographic printing plate P is sandwiched at its trailing edge to beconveyed to ejection portion 40. The ejection portion 40 is composed ofconveyance means such as a conveyance roller which ejects presensitizedlithographic printing plate P conveyed by presensitized plate ejectingmeans 39 out of enclosure 12 and a conveyance belt. Other constitutionelements identical to those in FIG. 2 are given the same symbols asthose in FIG. 2 to omit their explanation.

Next, operations of a unit shown in FIG. 3 will be explained as follows.The uppermost sheet among a plurality of presensitized lithographicprinting plates P stacked on feeding means 13 is fed out toward the leftside in the figure by the feeding means 13, and when it is conveyed byconveyance roller 14 to a prescribed position on the side of holdingmeans 31, the leading edge of the sheet is caught by presensitized platemounting means 34 and is lifted along the holding surface 32a up to thetop portion thereof. Then, pressure roll 35 presses presensitizedlithographic printing plate P against the holding surface 32a in thedirection perpendicular to that surface near the top end of the holdingsurface 32a. Concurrently with this, decompression is started by apressure-reducing means of holding means 31, then suction is carried outthrough evacuation hole 19, and almost simultaneously with this, thepressure roll 35 swings toward the bottom end of the holding surface 32awhile pressing presensitized lithographic printing plate P, thus, thepresensitized lithographic printing plate P is sucked on the holdingsurface 32a and is held thereon. After that, the pressure roll 35 leavesthe holding surface 32a, optical writing means 37 starts rotating athigh speed, and thereby exposure is carried out in accordance with imageinformation prepared separately. After completion of image exposure,means for irradiating on the full surface 38 irradiates active light onthe full surface, then decompression is released after completion of theirradiation on the full surface, thereby presensitized plate ejectingmeans 39 sandwiches the trailing edge of presensitized lithographicprinting plate P and rotates clockwise in the figure to transport thepresensitized lithographic printing plate P to ejection portion 40 wherethe presensitized lithographic printing plate P is ejected out ofenclosure 12.

In the units shown in FIG. 2 and FIG. 3, it is also possible to employthe constitution wherein holding is carried out under the condition thatthe pressure roll is not pressed against the holding surface. It ispreferable that the pressure roll is structured to have acircumferential surface around which an elastic object is wound. Rubberhardness of the elastic object which is not less than 40° is preferablefor the pressure roll to come in close contact uniformly, and it ispreferable for excellent close contact that line pressure of 1 kg/cm ormore is used for pressing the pressure roll. An optical writing meansmay also be composed of a plurality of lasers. Further, as a conveyancemeans, any means such as a roller, a belt or the like can be used. Inaddition, in a unit as that shown in FIG. 2, evacuation holes can alsobe opened and closed in synchronization with rotation of a holdingmember when holding.

(Processing)

In the present invention a developer used for processing thepresensitized lithographic printing plate (development) and areplenishing solution thereof contain alkali metal silicate. Alkalimetals of the silicate include lithium, sodium and potassium, and amongthese is preferable potassium.

It is preferable that, during the course of the development, a developerreplenishing solution is optimally replenished in accordance with theprocessing amount of the presensitized lithographic printing plate.

The developer and replenishing solution thereof each are preferably anaqueous alkali metal silicate solution having a ratio of SiO₂ !/ M! of0.5 to 2.0, preferably 0.15 to 1.0 (in which SiO₂ ! is a molarity ofSiO₂ and M! is a molarity of an alkali metal) and a SiO₂ concentrationof 0.5 to 5.0% by weight. More preferably, SiO₂ !/ M! and SiO₂concentration of the developer are 0.25 to 0.75 and 1.0 to 4.0,respectively; and SiO₂ !/ M! and SiO₂ concentration of the replenishingsolution is 0.15 to 0.50 and 1.0 to 3.0, respectively.

The developer and replenishing solution may contain a water-soluble oralkali-soluble organic or inorganic reducing agent.

Examples of the organic reducing agent include phenols such ashydroquinone, metol and metoquinone; and amine compounds such asphenylenediamine and phenylhydrazine. Examples of the inorganic reducingagent include sulfites such as sodium sulfite, potassium sulfite,ammonium sulfite, sodium hydrogen sulfite, potassium hydrogen sulfite;phosphites such as sodium phosphite, potassium phosphite, sodiumhydrogen phosphite, potassium hydrogen phosphite, sodium dihydrogenphosphite, and potassium dihydrogen phosphite; hydrazine, sodiumthiosulfate and sodium dithionite. The water-soluble or alkali-solublereducing agent maybe contained in the developer or replenishing solutionin an amount of 0.05 to 10% by weight.

The developer and the replenishing solution thereof may contain anorganic carboxylic acid.

The carboxylic acid includes an aliphatic carboxylic acid having 6 to 20carbon atoms and an aromatic carboxylic acid such as acarboxy-substituted benzene or naphthalene.

The aliphatic carboxylic acid is preferably an alkane acid having 6 to20 carbon atoms, including caproic acid, enathylic acid, caplyric acid,pelargon acid, capric acid latric acid, myristic acid palmitic acid andstearic acid; more preferably an alkane acid having 6 to 12 carbonatoms. The aliphatic acis may have a double bond or be branched. Thealiphatic carboxylic acid above-described may be used as sodium,potassium or ammonium salt.

Examples of the aromatic carboxylic acids include benzoic acid,o-chlorobenzoic acid, p-chlorobenzoic acid, o-hyroxybenzoic cid,p-hydroxybenzoic acid, p-tert-butylbenzoic acid, o-aminobenzoic acid,p-aminobenzoic acid, 2,4-dihydroxybenzoic acid, 2,5-dihydroxybenzoiccid, 2,6-dihydroxybenzoic acid, 2,3-dihydroxybenzoic cid,3,5-dihydroxybenzoic cid, gallic acid, 1-hydroxy-2-naphthoeic acid,3-hydroxy-2-naphthoeic acid, 2-hydroxy-1-naphthoeic acid, naphthoeicacid and 2-naphthoeic acid.

The aromatic carboxylic acid may be used as a sodium, potassium orammonium salt.

The aliphatic or aromatic carboxylic acid is contained in an amount of0.1 to 30% by weight.

The developer and the replenishing solution thereof may contain asurfactant including an anionic, nonionic or cationic surfactant, or anorganic solvent. The developer and replenishing solution thereof mayfurther contain additive known in the art.

EXAMPLES

The method of preparing the lithographic printing plate of the presentinvention will be explained on the basis of examples thereof, but theembodiment of the present invention is not limited thereto. Hereinafter,the word, "part(s)" refers to weight part(s).

Example 1

Preparation of grained aluminum plate:

An aluminum plate having a thickness of 0.24 mm was dipped in a sodiumhydroxide aqueous solution for degreasing, washed and subjected toelectrolytic etching for 5 min. in 1% hydrochloric acid aqueous solutionat 25° C. and a current density of 3 A/dm². After being washed, theplate was dipped in a 0.9% sodium hydroxide aqueous solution and thenwashed. Subsequently, the plate was subjected to anodic oxidation for 2min. in 40% sulfuric acid aqueous solution at 30° C. and a currentdensity of 1.5 A/dm² and washed. The plate was further dipped in a 1%sodium metasilicate aqueous solution at 80° C. over a period of 30 sec.for sealing treatment, washed and dried to obtain an aluminum plate foruse as a support of the presensitized lithographic printing plate.

Coating of photosensitive layer coating solution:

On the aluminum plate prepared as above-described, a coating solution ofa positive-working photosensitive layer having the following compositionwas coated with a rotary coating machine. The coating amount of thephotosensitive layer (1) was 2.2 g/m².

Positive-working photosensitive layer coating solution (1):

    ______________________________________    Novolak resin 1          7.0    g    o-Naphthoquinonediazide compound (QD1)                             1.4    g    Halomethyloxadiazole compound (rad1)                             0.05   g    Pictorial pure blue (trade name, dye                             0.07   g    product by Hodogaya Kagaku)    Methyl cellosolve        100    ml    ______________________________________

Novolak resin 1: A condensation copolymer of phenol, m-cresol, p-cresoland formaldehyde (molar ratio of phenol, m-cresol and p-cresol,2.0:4.8:3.2; Mw=6000, Mw/mn=5.0). ##STR34## Coating of ablatablelight-shielding layer coating solution 1:

On the photosensitive layer above-prepared, a light-shielding layercoating solution 1 containing the following composition was coated usinga wire-bar and dried to form an ablatable light-shielding layer (1)having a thickness of 0.5 μm. There was thus obtained a presensitizedlithographic printing plate.

Light-shielding layer coating solution 1:

    ______________________________________    Gelatin             2.9 parts    Near-infrared absorbing dye (IR-1)                        0.8 parts    Colloidal silver    1.6 parts    Water               94.7 parts    ______________________________________

Ablation of ablatable light-shielding layer:

The presensitized lithographic printing plate was exposed to laser beamfrom semiconductor laser LT090MD (product by Shrap, wavelength of 830nm, maximum light output of 100 mW). The light-shielding layer wasablated by scanning with a condensed spot having a diameter of 6 μm at ascanning speed of 0.5 m/sec. (Optical efficiency was 60%.) Ablatedportions which were in a dot form had a dot size of 6.5 μm in diameter.Further, the laser was modulated through RIP and a pattern exposure wasmade through a 175-lines screen by changing a dot percentage atintervals of 10% in a range of from 0 to 100%.

The thus pattern-ablated presensitized plate was overall exposed over aperiod of 70 sec. at 90 cm far apart from a light source of 2 kW metalhalide lamp (product by Iwasaki Electric Co., Idlefin 200).

Next, the sample was develpoed at 25° C. for 30 sec. with a developerwhich was prepared by diluting a developer SDP-1 (product by Konica) by7 to 9 times. As a result, development was proved to be good.

Further, plate life test was conducted using a sheet-fed press, so thatthe plate life was shown to be 200,000 sheets, wherein the plate lifewas referred to as the number of printed sheet at which a printed imagebecame ink-deficient or blurred.

Example 2

A presensitized lithographic printing plate was prepared by coating, onthe grained aluminum plate which was the same as used in Example 1, acoating solution of a negative-working photosensitive layer having thefollowing composition in a similar manner to Example 1 to form aphotosensitive layer (2) and futher thereon, coating a coating solutionof a light-shielding layer in a similar manner to Example 1 to form anablatable light-shielding layer (2).

Negative-working photosensitive layer coating solution (2):

    ______________________________________    Diazonium resin 1       1 g    Polymer compound 1      10 g    Polyacrylic acid (Julimer Ac-10L,                            0.6 g    product by Nihon Junyaku)    Pictorial pure blue BOH (Hodogaya Kagaku)                            0.2 g    Methyl cellosolve       160 g    ______________________________________

Diazonium resin was prepared in the following manner.

p-Diazodiphenylamine sulfate of 14.5 g (50 mmol) was dissolved inconcentrated sulfuric acid solution of 40.9 g with ice-cooling. Aftercompleting the reaction, para-formaldehyde of 1.5 g (50 mmol) was slowlyadded dropwise thereto, while being kept at a temperature of 10° C. orlower. The reaction mixture was stirred further for 2 hrs. withice-cooling. The reaction product was added dropwise to ethanol of 500ml with ice-cooling and resulting precipitate was separated byfiltration. The precipitate was washed with ethnol and dissolved inwater of 100 ml. To the aqueous solution was added a cooled,concentrated aqueous solution in which zinc chloride of 6.8 g wasdissolved. The resulting precipitate was separated by filtration, washedwith ethanol and dissolved in water of 159 ml. To this solution wasadded a cooled concentrated aqueous solution in which ammoniumhexafluorophosphate of 8 g was dissolved. The resuting precipitate wasseparated by filtration, washed with water and dried at a temperature of30° C. over a period of one day and night to obtain 1 g of diazoniumresin. The resin was subjected to GPC for determining a molecularweight, and it was shown to have a weight-averaged molecular weight of2400. Polymer compound 1 was prepared in the following manner.

    ______________________________________    N-(4hydroxyphenyl)methacryl amide                         10.3 g    Acrylonitrile        15.9 g    Ethyl acrylate       55 g    Methacrylic acid     8.6 g    ______________________________________

and azobisisobutylonirile (AIBN) of 1.6 g were dissolved in 110 ml of amixed solvent of acetone and methanol in a ration of 1:1 and allowed tobe reacted by heating at 60° C. for a period of 8 hrs. under anatmosphere of nitrogen gas. After completion of reaction, the reactionmixture was poured into water of 5 liters. The resuting precipitate(white-colored) was separated by filtration and dried to obtain polymercompound 1 of 75 g. From the melecular weight measurement (GPC), it wasshown to have a weight-averaged molecular weight of 92,000.

Next, a coating solution of an ablatable light-shielding layer havingthe following composition was coated on a photosensitive layer in asimilar manner to Example 1.

Light-shielding layer coating solution 2

    ______________________________________    Gelatin                     2.5 parts    Near-infrared absorbing dye (IR-1)                                1.2 parts    Carbon black aqueous dispersion                                4.3 parts    (containing carbon black of 1.2 parts)    (DISPERSE BLACK SD9020 produced by Dainihon Ink Co.,:    carbon blach, 30% and dispersing agent, 10%)    Water                        92 parts    ______________________________________

The thus-obtained presensitized lithographic printing plate wasimagewise exposed to laser beam in the same manner as in Example 1,further overall exposed for 45 sec. and developed at 25° C. for 45 sec.with a developer which was prepared by diluting a developer SDN-21(product by Konica) by 4 times. It was shown that developbility wasexcellent without print-stain and plate life was 150,000 sheets.

Example 3

On a grained aluminum plate, a coating solution of a negative-workingphotosensitive layer having the following composition was coated in asimilar manner to Example 1 to obtain a photosensitive layer (3).

Negative-working photosensitive composition coating solution (3)

    ______________________________________    Diazonium resin 1           0.48   g    Polymer compound 2          6      g    Trimethylolpropanetriacrylate                                6      g    Photopolymerization initiator                                0.6    g     ##STR35##    Polyacrylate (Julimer Ac-10L produced by Nihon Junyaku)                                0.24   g    Pictorial pure blue BOH (product by Hodogaya Kagaku Co.)                                0.24   g    Methyl cellosolve           160    g    ______________________________________

Polymer compound 2 was prepared in the following manner.

    ______________________________________    N-(4hydroxyphenyl)methacryl amide                          35 g    Acrylonitrile         10 g    Methyl methaacrylate  34 g    Methacrylic acid       6 g    ______________________________________

and azobisisobutylonirile (AIBN) of 1.2 g were dissolved in 80 ml of amixed solvent of acetone and methanol in a ratio of 1:1 and allowed tobe reacted by heating at 60° C. for a period of 8 hrs. under anatmosphere of nitrogen gas. After completion of the reaction, thereaction mixture was poured into water of 5 liter. The resutingprecipitate (white-colored) was separated by filtration and dried toobtain polymer compound 2 of 75 g. From the melecular weight measurement(GPC), it was shown to have a weight-averaged molecular weight of40,000.

Next, A presensitized lithographic printing plate was prepared bycoating the light-shielding layer coating solution 1 afore-described inthe same manner as in Example 1 to form an ablatable light-shieldinglayer having a thickness of 0.7 μm. The presensitized lithographicprinting plate was imagewise exposed to laser light and thenoverall-exposed for 45 sec. in a similar manner to Example 1. Ater beingdipped in a developer having the following composition, the surface ofthe plate was lightly rubbed with absorbent cotton to remove anunexposed portion.

Developer:

    ______________________________________    Benzyl alcohol           28     g    Triethanolamine          13     g    Sodium sulfite           2      g    Alkylphenylpolyethylene glycol ether                             10     g    Water                    955    g    ______________________________________

As a result thereof, it was shown that developability was excellent,without press stain and the plate life was 130,000 sheets.

Example 4

An experiments was carried out in a similar manner to Example 1,provided that the composition of the light-shielding layer was varied asshown in Table 1 (Samples Nos.4-1, 4-3, 4-5 and 4-6). Further, anotherexperiment was carried out in a similar manner to Example 2, providedthat the composition of the light-shielding layer was varied as shown inTable 1 (Samples Nos. 4-2 and 4-4).

Coating solution compositions of the light-shielding layer, 3, 4, Comp.1to 3 are as follows.

Light-shielding layer composition 3:

    __________________________________________________________________________    Water soluble polyester resin (anionic, pH, 3-5) (PES resin 200, 20%                                   10.                                      parts    solution, produced by Takamatsu Yushi)    Cadmium yellow                 1.2                                      parts    Near-infrared absorbing dye (IR-2)                                   1.8                                      parts    Polyoxyethyleneoleyl phosphate 0.1                                      parts    Water                          86.9                                      parts    __________________________________________________________________________     IR-2:     ##STR36##    -  Light-shielding layer composition 4:

    __________________________________________________________________________    Methylcellulose resin (SM 400 product by Shinetsu Kagaku)                                1.8 parts    Hanza yellow                1.2 parts    Triethnolamine oleyl soap   0.1 parts    Near-infrared absorbing dye (IR-3)                                2   parts    Water                       94.9                                    parts    __________________________________________________________________________     IR-3     ##STR37##    -  Light-shielding layer composition (Comp. 1):

    ______________________________________    Carbon black          2     parts    Nitrocellulose        1.4   parts    Alkyd resin           4.6   parts    Methyl ethyl ketone   92    parts    ______________________________________

Light-shielding layer composition (Comp. 2):

    __________________________________________________________________________    Nitrocellulose       2      parts    Near-infrared absorbing dye (IR-4)                         1.8    parts    Cadmium yellow       1.2    parts    Methyl cellosolve    95     parts    __________________________________________________________________________     IR-4     ##STR38##    -  Light-shielding layer composition (Comp. 3):

    ______________________________________    Gelatin                   1.5    parts    Carbon black aqueous dispersion                              5.0    parts    (including 1.5 parts of carbon black)    (DISPERSE BLACK SD9020: carbon black, 30% and    dispersing agent, 10%)    Water                     93.5   parts    ______________________________________

                  TABLE 1    ______________________________________           Light-shielding    Photo-   layer    Sam- sensi-           Thick-    ple  tive    Compo-   ness  develop-                                       plate life                                               Re-    No.  layer   sition   (μm)                                ability                                       (sheets)                                               marks    ______________________________________    4-1  (1)     3        0.7   Good   200,000 Inv.    4-2  (2)     3        0.7   Good   150,000 Inv.    4-3  (1)     4        0.7   Good   200,000 Inv.    4-4  (2)     Comp. 1  1.0   No good *                                       Not printable                                               Comp.    4-5  (1)     Comp. 2  0.5   Stain  Not printable                                               Comp.    4-6  (1)     Comp. 3  0.6   Stain  Not printable                                               Comp.    ______________________________________     * Line with reduction

In samples 4-4 and 4-5, the light-shielding layer peeled away from theupper-side of the photosensitive layer during development and remainedin a developer, as a insoluble residue. When observing ablated portionsof developed samples 4-4 to 6, it was shown that carbon black was weldedwith the photosensitive layer, so that the photosensitive layer was notcompletely removed.

Example 5

A coating solution of a light-shielding layer was prepared accoding tothe formula as described below. A photosensitive layer and alight-shielding layer were each coated in this order on a grainedaluminum plate in the same manner as in Example 1.

Photosensitive layer:

A solution of the photosensitive layer, which was the same as in Example1 was coated so as to have a thickness of dried coating of 2.0 μm bymeans of wire-bar.

Light-shielding layer:

The following solutions A and B for the light-shielding layer weredispersed according to the procedure as described below, and theresulting dispersion was mixed with a solution C for the light-shieldinglayer to prepare a coating solution of the light-shielding layer. Thecoating solution was coated on the photosensitive layer by a wire-bar soas to have a thickness of dried coating of 0.6 μm.

    ______________________________________    Solution A for light-shielding layer:    Near-infrared absorbing dye (IR820B, product                             7      parts    by Nihon kayaku)    Di-2-ethylhexylphthalate (product by Kantoh                             7      parts    Kagaku)    Methyl ethyl ketone      86     parts    Solution B for light-shielding layer:    Ossein gelatin           8      parts    Surfactant (Alkanol XC, product by du'Pont)                             2      parts    Water                    90     parts    Solution C for light-shielding layer:    Surfactant (surf-1)      0.1    parts    Gelatin                  6.1    parts    Colloidal silver         3.8    parts    Water                    90     parts    ______________________________________     Surf-1:     ##STR39##

Solutions A and B each were stirred with a stirrer (50 rpm), under tightsealing, at 50° C. over a period of 20 min.

Solution A was slowly added dropwise to Solution B in a weight ratio ofSolution A to B of 2:5., while a vessel containing Solution B wasmaintained at 4° to 8° C. by cooling with ice water, stirred with astirrer (30 rpm) and dispersed with a ultra-sonic homogenizer.

The resulting dispersion (a mixed solution of Solutions A and B) wasmixed with Solution C in a weight ratio of 1:1 with stirring to preparea coating solution of the light-shielding layer.

The thus-prepared presensitized lithographic printing plate was exposedto infrared laser light and UV radiation, developed and evaluated in amanner similar to Example 1. The result thereof was excellent indevelopability and the plate life was proved to be 200,000 sheets.

Example 6

A presensitized lithographic printing plate was prepared in the samemanner as Example 5, except that a near-infrared absorbing dye, G022(product by Nihon Kayaku) was employed in place of a dye IR820B. Thethus-prepared presensitized lithographic printing plate was exposed toYAG laser (50 W) and UV radiation, developed and was evaluated withrespect to the printing test in a similar manner to Example 1. Theresult thereof was excellent in developability and the plate life wasproved to be 200,000 sheets.

Example 7

A presensitized lithographic printing plate which was prepared inExample 1 was exposed to laser light according to the following exposurecondition, and compared with each other with respect to ablatability.Results thereof are shown in Table 2.

                  TABLE 2    ______________________________________    Laser Spot   Optical               Ablated    output          diam-  effi-   Power  Exposure                                       hole    power eter   ciency  density                                speed  diameter                                              Develop-    (mW)  (μm)                 (%)     (W/cm.sup.2)                                (m/sec.)                                       (μm)                                              ability    ______________________________________    500   10     50      318000 2      11     Good    500   25     50       50000 0.3     0     No good    ______________________________________

As can be seen from Table 2, in the case where the power density at theexposed surface was low, ablation was insufficient even when theexposure speed was made lowered so that am image was not formed.

Example 8

A photosensitive layer was coated on a grained aluminum plate in asimilar manner to Example 1.

(Coating of interlayer)

A coating solution for an interlayer having the following compositionwas coated on the photosensitive layer with a wire-bar and dried toprovide an interlayer having a dry thickness of 2 mm.

Interlayer coating solution 1

    ______________________________________    Novolak resin-1  20 parts    Methyl ethyl ketone                     80 parts    ______________________________________

(Coating of ablatable light-shielding layer)

Next, a coating solution for an ablatable light-shieling layer havingthe folowing composition was coated on the interlayer with a wire-barand dried to form an ablatable light-shielding layer having a thicknessof 0.8 mm and obtain a presensitized lithographic printing plate sample1.

Light-shielding layer coating solution 1

    ______________________________________    Gelatin             2.3        parts    Near-infrared absorbing dye (IR-1)                        1.4        parts    Colloidal silver    0.8        parts    Water               95.5       parts    ______________________________________     IR-1     ##STR40##    -  (Image formation)

Ablation of light-shielding layer:

The thus-prepared presensitized lithographic printing plate was exposedto laser from semiconductor laser LT090MD (product by Sharp, wavelengthof 830 nm, maximum light output of 100 mW. The light-shielding layer wasablated by scanning with a condensed spot having a diameter of 6 μm at ascanning speed of 1.3 m/sec. (Optical efficiency was 60%.) Ablatedportions which were each in a dot form had a dot size of 6.5 μm indiameter. Further, the laser was modulated through RIP and a patternexposure was made through a 175-lines screen by changing a dotpercentage at intervals of 10% in a range of from 0 to 100%.

Exposure of photosensitive layer:

The thus-ablated plate was overall exposed for 70 sec. at 90 cm farapart from a light source of 2 kW metal halide lamp (productIwasakielectric Co., Idlufin 200).

Development:

Next, the exposed sample was developed at 25° C. for 30 sec. with adeveloper which was prepared by diluting a developer SDP-1 (product byKonica) by 7 to 9 timed. Resultingly, development was proved to be good.

Printing:

The printing was conducted using a sheet-fed press, so that the platelife was shown to be 150,000 sheets.

Example 9

A photosensitive layer was coated on a grained aluminum plate in asimilar manner to Example 1.

Coating of light-heat converting layer:

Next, a coating solution for a light-heat converting layer having thefollowing composition was coated on the photosensitive layer with awire-bar and dried to form a light-heat converting layer with athickness of 0.3 μm

Light-heat converting layer coating solution

    ______________________________________    Gelatin             2.4        parts    Near-infrared absorbing dye (IR-1)                        1.6        parts    Water               96.0       parts    ______________________________________     IR-1     ##STR41##

In the case when the coating solution for the light-converting layer ona transparent PET (polyethylene terephthalate) base in a similar mannerto the above, an absorbance thereof was 88% and 7% at 830 nm and 400 nm,respectively.

Coating of light-shielding layer:

The following light-shielding layer was coated on the light-heatonverting layer above-described wit a wire-bar and dried to form alight-shieling layer with a thickness of 0.6 μm. Thus, apositive-working presensitized lithographic printing plate was pepared.

Light-shielding layer coating solution:

    ______________________________________    Novolak resin-1          0.8 parts    Red iron oxide TF 100 (product by Toda Kogyo)                             4.1 parts    CAFACRE-610 (product by Toho Kagaku)                             0.1 parts    Methyl ethyl ketone      95.0 parts    ______________________________________

In the case when this coating solution for the light-shielding layer wascoated on a transparent PET base in a similar manner to the above, anabsorbance thereof was shown to be 19% and 99.1% at 830 nm and 400 nm,respectively.

Laser exposure:

The thus-prepared presensitized lithographic printing plate was exposedto laser light from semiconductor laser LT090MD (product by Sharp,wavelength of 830 nm, maximum light output of 100 mW. Thelight-shielding layer was ablated by scanning with a condensed spothaving a diameter of 6 μm at a scanning speed of 1.3 m/sec. (Opticalefficiency was 60%.) Ablated portions which were in a dot form had adotsize of 6.5 μm in diameter. Further, the laser was modulated through RIPand a pattern exposure was made through a 175-line screen by changing adot percentage at intervals of 10% in a range of from 0 to 100%.

Exposure of photosensitive layer:

The thus-ablated plate was overall exposed for 70 sec. at a position of90 cm far from a light source of 2 kW metal halide lamp (productIwasakielectric Co., Idlufin 200).

Development:

Next, the exposed sample was developed at 25° C. for 30 sec. with adeveloper which was prepared by diluting a developer SDP-1 (product byKonica) by 7 to 9 timed. Resultingly, development was proved to be good.

Printing:

The printing was conducted using a sheet-fed press, so that the platelife was shown to be 150,000 sheets.

According to the present invention, it is possible to prepare alithographic printing plate directly from digital imge signals withoutthe use of a film which is employed as an intermediate in theplate-making process; a method for preparing a lithographic printingplate directly from digital image signals is provided, wherein aablatable light-shielding layer, which can be industrially preparedreadily and at a moderate price, can be removed sufficiently during aprocess of development without the need of removing a masking layer atan unexposed portion and adverse effect on a photosensitive layer.

What is claimed is:
 1. A method for preparing a lithographic printingplate by a process comprising the steps ofimagewise exposing apresensitized lithographic printing plate, comprising a support havingthereon a photosensitive layer and an ablatable and water-soluble oraqueous alkali-soluble light-shielding layer containing a water-solubleor aqueous alkali-soluble resin, to a first light having a firstwavelength, to remove the imagewise exposed portion of thelight-shielding layer by ablation, overall exposing the presensitizedplate to a second light having a second wavelength to expose thephotosensitive layer at portions in which the light-shielding layer hasbeen removed and developing the overall exposed plate with a developerto remove the unremoved water soluble or aqueous alkali-solublelight-shielding layer and a non-imaging portion of the photosensitivelayer to obtain the lithographic printing plate, wherein saidlight-shielding layer substantially cuts off the second light having thesecond wavelength to prevent a photochemical reaction from occurring insaid photosensitive layer, said photosensitive layer photochemicallyreacting in response to the second light and containing ano-quinonediazide compound or a diazo compound.
 2. The method forpreparing a lithographic printing plate of claim 1, wherein saidlight-shielding layer contains a light-heat converting substance capableof causing conversion of light into heat upon absorption of the firstlight and a substance capable of absorbing the second light.
 3. Themethod for preparing a lithographic printing plate of claim 1, whereinsaid light-shielding layer comprises a light-heat converting layercapable of converting light to heat upon absorption of the first lightand a shielding layer capable of shielding said photosensitive layerfrom the second light.
 4. The method for preparing a lithographicprinting plate of claim 1, wherein said presensitized plate has aninterlayer provided between said photosensitive layer andlight-shielding layer.
 5. The method for preparing a lithographicprinting plate of claim 1, wherein said first light is a laser lighthaving a power density of 100000 W/cm² or more, being exposed at anexposing speeed of 0.4 m/sec. or more.
 6. The method for preparing alithographic printing plate of claim 1, said second light is aultraviolet radiation.
 7. The method for preparing a lithographicprinting plate of claim 1, wherein said first wavelength is not lessthan 500 nm and said second wavelength is less than 500 nm.
 8. Themethod for preparing a lithographic printing plate of claim 1, whereinsaid light-shielding layer absorbs 80% or more of the first light. 9.The method for preparing a lithographic printing plate of claim 1,wherein said light-shielding layer absorbs 97% or more of the secondlight.
 10. A presensitized lithographic printing plate comprising asupport having thereon a photosensitive layer and an ablatablelight-shielding layer capable of absorbing a laser light and a light towhich said photosensitive layer is sensitive, said light-shielding layerbeing water-soluble or aqueous alkali-soluble and comprising a substancecapable of absorbing a laser light, a substance capable of absorbing alight to which said photosensitive layer is sensitive and awater-soluble or aqueous alkali-soluble resin; said photosensitive layercontaining an o-quinonediazide compound or a diazo compound.
 11. Thepresensitized lithographic printing plate of claim 10, wherein saidlight-shielding layer contains a near infrared absorbing dye as thesubstance capable of absorbing a laser light and a water-soluble resin.12. The presensitized lithographic printing plate of claim 10, whereinsaid photosensitive layer contains said o-quinonediazide compound. 13.The presensitized lithographic printing plate of claim 10, wherein saidphotosensitive layer contains said diazo compound.
 14. The presensitizedlithographic printing plate of claim 12, wherein said near infraredabsorbing dye is water-soluble.
 15. The presensitized lithographicprinting plate of claim 11, wherein said photosensitive layer contains ao-quinonediazide compound.
 16. The presensitized lithographic printingplate of claim 12, wherein said photosensitive layer contains a diazocompound.